ground loop (I think?) problem

[Jakeman1086]

I know very little about circuits, so I really need your help.

The picture represents exactly what my setup consists of right now.

I have high frequency "chirping" noises coming from the speakers that tend to react to mouse clicks and cpu activity. I completely solved the problem for a single speaker by inserting an IMP2 DI Box Whirlwind / Direct Boxes in between my audio interface and that studio monitor. The volume was significantly reduced and I think I might be losing high frequency content though.

I'm thinking the problem is interference between the CPU and the firewire connection which are very close to each other on the motherboard. Dunno.

What should I do?

*buy a PCI card with firewire to get the firewire connection farther away from the CPU?
*use ground-loop solving strategies (telescoping, etc.)? Please be specific. I know very little about the subject.

[Jakeman1086]

UPDATE:

The noise significantly reduced when I plugged my audio interface's AC adapter into it.

When I listened through some headphones on the headphone output of the Presonus Firebox, there was zero noise. I was told that because of this, it is definitely a ground loop due to a voltage on the ground between my powered monitors and pc/interface

Here is the noise I'm talking about:

[SAC]

I am well versed in ground issues, but I must admit to being completely confused by the description here, let alone by the description of addressing interference between a CPU and Firewire I/O due to a ground loop...
Induced interference from a Firewire circuit into a CPU is neither ground-loop interference - nor the sign of a decent computer! If this is even a viable possibility, I would get a new computer - preferably with internal components from some other manufacturer!!!
...might you mean ground loop noise between your computer and the mic pre-amp?

I would suggest that you actually identify the nature and source of the problem and resolve it rather than looking for magic 'parts' to mask the problem. It makes no sense to randomly begin searching for solutions when the specific problem has not been isolated and identified.

You might start with Bill Whitlock's Understanding, Finding and Eliminating ground Loops

http://www.jensen-transformers.com/a...%20seminar.pdf

and his Troubleshooting Guide available at

http://www.jensen-transformers.com/an/ts_guide.pdf

Another good overview is Jim Brown's: Power and Grounding for Audio and Audio/Video Systems - A White Paper for the Real World

http://www.audiosystemsgroup.com/SurgeXPowerGround.pdf

There are not going to be any quick-fix answers as alternatives to actually walking through the trouble shooting process...if this is indeed the problem

And if it is a 'Pin 1' problem, there are a number of good tutorials available from Neil Muncy, Jim Brown, Bill Whitlock, Mary Gruszka, Pat Brown and others...

Here are two quick links to Mary's excellent articles based upon Neil's pioneering work:

The Pin-1 Problem, by Mary C. Gruszka

How to Test for Pin 1 Problems, by Mary C. Gruszka

Resolving Pin-1 Problems, by Mary C. Gruszka

And one additional paper that addresses the subject well, also by Jim Brown:

Pin1 Revisited

BTW, the PreSonus Firebox has been known to exhibit pin1 problems.

Oh, and one more thing - especially after I said there were no 'quick-fix' solutions to fundamental design integrity...
Please be sure you are using the new Neutrik EMC series of balanced connectors!
The NC3FXX-EMC (B),NC3MXX-EMC & NC3FDX-EMC-Spec
These WILL help make a difference as they are a direct result of Neil Muncy's analysis of the issue. (See Pin1 Revisited)


...Hope that helps...

[DanDan]

Great post SAC. Those simple explanations by Mary blew away my cobwebs on this matter. Thanks and Happy New Year.

Jakeman HNY to you too. What speakers are you using? Are you using balanced screened cable or is it Speaker cable? Plastic or metal jacks? Some more details and we will sort this out for you.
DD

[TRANQUILO]

remove all Un-balanced cables and use balanced cables. use transformers when mixing un-balanced and balanced connections. If youre not shure what is what look at the manuals of your equipment.
Also try using one of those little gray or orange adapters on your eqipment and powerstrip that disables the ground(meant for old two prong outlets). So in other words dis-connect the ground on your powerstrip so its not connected to your grounding system of your buliding. I had a the exact same problem. I ripped the ground prong off and presto quiet as a sleeping baby! And if youre worried about not having a ground use a GFCI or AFCI recepticle or Circuit breaker of that type. A GFCI is code compliant when no ground is present. It stands for "ground fault circuit interupter" which shuts off power if a ground fault is detected. Protect your stuff!!!

[Tonio Ruiz]

Originally Posted by TRANQUILO

remove all Un-balanced cables and use balanced cables. use transformers when mixing un-balanced and balanced connections. If youre not shure what is what look at the manuals of your equipment.
Also try using one of those little gray or orange adapters on your eqipment and powerstrip that disables the ground(meant for old two prong outlets). So in other words dis-connect the ground on your powerstrip so its not connected to your grounding system of your buliding. I had a the exact same problem. I ripped the ground prong off and presto quiet as a sleeping baby! And if youre worried about not having a ground use a GFCI or AFCI recepticle or Circuit breaker of that type. A GFCI is code compliant when no ground is present. It stands for "ground fault circuit interupter" which shuts off power if a ground fault is detected. Protect your stuff!!!

I apologize for kidnaping this nice thread for a bit

all if the info shared in this thread is wonderful, I also have a couple of ground issues at my studio that I haven't been able to solve, one of them is a low hum noise that appears when I turn up 1 of my Motu HD192 cards, it's driving me crazy cause I can't figure it out, I've tried using the orange adapters on different pieces of gear, different switches or power lines, nada, nothing works

one question though, I have NS10 monitors along with a Yamaha Power Amp for them, what kind of speaker cable shall I'd using with this? cause right now I'm just using regular speaker cable like the home audio type

just for the record, all of my cables are Belden/Gotham and Neutrik conectors

Happy New Year everyone!!!!

[PaulP]

Originally Posted by TRANQUILO

Also try using one of those little gray or orange adapters on your eqipment and powerstrip that disables the ground(meant for old two prong outlets). So in other words dis-connect the ground on your powerstrip so its not connected to your grounding system of your buliding.

I wouldn't do this, GFCI or not. What if the equipment is used somewhere
else ? If you have a ground loop there are proper ways of fixing it without
disabling your main safety mechanism.

You really don't want to electrocute someone .

Paul P

[SAC]

PaulP is absolutely correct!

A ground lift is NOT a solution to the problem!

All it is is akin to disabling a fault indicator light - or closing your eyes and thinking the problem has gone away!

PLEASE read and understand the Whitlock presentation.

BTW, the PPT of the Whitlock presentation is the same on used at the (literally) most heavily attended seminar each year at AES!

I cannot stress this enough: What he says in not simply 'one guy's opinion' - it is pretty near gospel from one of THE gurus of the subject! There is a good reason that he, Neil Muncy and Jim Brown are the perennial presenters on this subject every year at AES!

Please folks, I am just the messenger.

And this is one topic that does NOT bears a bunch of folks speculating here. This subject is WELL UNDERSTOOD. And the Whitlock, Brown and Muncy triad are considered among the BEST in the field - period. Check out their credential in AES for a start.

Their 'best practices' list is the industry standard.

[DanDan]

I reckon this little issue needs to be considered from the ground up
Jakeman, some details please?
If you cables from MOTU are Speaker cable you need to change them to screened signal cable.

DD

[SAC]

First, and quite simply, if your building has multiple ground paths - electrical, CATV, satellite, etc., etc. etc., you have a ground loop issue.

If they are not ALL grounded to a COMMON POINT ("common bonded"), there is a problem. ...And according to current electrical code (at least in the US), you are in violation!

You may not be currently experiencing it, but it exists nonetheless.

Once the electrical integrity of the premises is addressed, THEN you get to deal with the manner in which the equipment itself is built. And this presents a much more pervasive issue - one that has come to be known collectively as the "pin 1" problem...and that quite simply is the way the signal within the equipment 'relates' to ground.

As I 'suggested', review the Whitlock presentation. it covers it all. And then after all is secure there, then move on to the Pin 1 documents to start dealing with your equipment interconnects in order to resolve the issues in the PROPER way that will not simply mask a problem leaving you with a very potentially deadly situation.

And NO ground lifts! Well... except for those of you who still believe that if you close your eyes, no one can see you.

There is a fundamental difference between masking problems and solving them.

[John Suitcase]

I've had good luck with the Radio Shack Ground Loop Isolator.

I was having some noise issues when using the audio outputs on my iMac with an external hard drive. Solved that.

How far away is your Presonus unit from your computer? Does moving it around change the interference sounds?

Does the Presonus unit have a three prong AC adapter?

You could also try another power strip. It seems that some cheaper ones don't do a very good job with noise.

[Jakeman1086]

I strongly appreciate all your help. I had to turn my back on this problem for several months now due to other life issues that arose. But, I am ready to tackle this thing head on, and will follow any instructions given to get there.

First off, please ignore some of the weird things I described in the first post. I didn't know enough about the issue and was hoping for a quick fix.

SAC, I read those documents (all but the very long, technical one which I will when I get time). The pin-1 problem sounds like a likely culprit. The test methodology Bill Whitlock describes sounds good, but I don't know where to obtain a dummy, not to mention it doesn't seem like I have all too many things in my signal chain.

Attached I have provided a grand summary that includes EVERY detail I could possibly think of to help in detecting this problem. If you have the time, I could really use the help!

If you have any questions or wish me to perform any further tests, don't hesitate to ask! Thank you.

[SAC]

If I may make a suggestion.

Go through the defined troubleshooting steps one by one. Cherry picking and guessing will NOT do it! The procedure was developed by the best in the industry for a reason! *

Also, my first guess is that you have much more connected then your diagram indicates.

AC lines are NOT the only signal paths in play here. Telephone, satellite TV, cable TV/Internet ALL have ground paths.

And as you will find in the troubleshooting steps, ALL of those signal sources MUST be common bonded at the same point.

Begin by having your electrical company respond and verify their ground. Also have them show you where the AC service ground is attached. This will be THE reference point.You will need to know this for the other services as they will need to relocate their grounds (as necessary) to attach at the same point.

You may as well begin by getting your your service providers out there now and verify that their services are common bonded. Have them remove the additional ground rods or separate grounds straps, etc and MAKE SURE that each service is common bonded (the ground attached to the same point) as that of your AC service.

They may balk a bit depending upon who you talk to, but it is a code requirement and they will if you stand your ground. Rather than call them and tell them they need to check their ground, you may just want to use another less explicit reason to get them out, as they may try to solve the issue over the phone or save the trip by symptom resolution instead of verifying the ground. And when they show up, accompany them and have them show you their ground and walk the service to verify that there are no other grounds.

If they have separate ground paths, you have a ground loop whether it is resulting in apparent signal degradation or not. And note, lifting grounds with a cheater plug is NOT the answer - but it is a great way to get electrocuted - especially during a storm while talking on the phone!

*Pin 1 issues are to be examined AFTER all ofthe AC and additional service ground paths are examined! It makes no sense to jump to pin 1 issues without completing your due diligence regarding the other service providers. Pin 1 issues (& SCIN issues) are with regard to balanced lines - and your computer and many other peripherals are not balanced!

[Jakeman1086]

Okay, so tomorrow I will be calling up:

a - TXU, my power company
b - AT&T, my internet/tv provider (no land line phone)

I will have TXU send someone by to identify and show me the AC ground for my house. I will have AT&T send someone by to remove all extra grounds, and just keep (or make) the ground that is shared by the AC service.

One thing I do not understand. If all my audio components are plugged into the same ac power strip, which is then plugged into a single ac outlet, how do the extra service grounds create a ground loop that can be heard in my audio system?

Thanks.

[SAC]

Originally Posted by Jakeman1086

One thing I do not understand. If all my audio components are plugged into the same ac power strip, which is then plugged into a single ac outlet, how do the extra service grounds create a ground loop that can be heard in my audio system?

Thanks.

Is your computer connected to the phone line and the Internet? or an external antenna for video or any other 'feed'? I ask as all of these are 'external' sources for ground loops as well.

Additionally, the various ways electronics observe polarity and internal grounding is 'fascinating' in a Frankenstein sort of way. And the 'internal' topology becomes a bit more complex in all of the myriad variations.

At a later point, you might want to very systematically eliminate one component at a time and see if one of them is the 'cause' of the problem... But one thing at a time.

Pull out the Whitlock troubleshooting guide...
As you will discover, your problem may not be limited to your 'strip' (if only things were as simple as selecting a convenient place at which to define the extent of the circuit!); but to all of the devices on the circuit, and possibly to your entire breaker box - meaning that it can extend to your entire house. Thus the reason to systematically review the topology of your circuitry. And to narrow the issue down from there.

Also, you may want to spend ~$5 at a local Home Depot and get a 3 prong outlet analyzer to check ground and polarity in the various outlets throughout the house.

[Jakeman1086]

My setup is not connected to the internet or any wireless service. The tests I performed were all done with this bare-bones setup (some of the tests reduced the setup to just the audio interface and computer - nothing else connected at all).

It makes sense what you're saying about 'anything in the house could be the culprit.' It makes sense that I would simplify the problem from the more general house grounding issue first.

One more question though. Whitlock's guide states this:

If the noise is unaffected by the setting of a volume control or selector, it must be entering the signal path after that
control.

I do not fully understand the concept of 'after' as this is all related to a loop (where does it start/end?). But, in my setup, the audio interface's volume knob has no effect whatsoever on the volume of the noise. The studio monitor's volume knob DOES affect the volume of the noise however. As the studio monitor and audio interface are directly connected via a 1/4" cable, would this mean the noise is entering the signal between the two?

Thanks again for your help.

[DanDan]

I do not fully understand the concept of 'after' as this is all related to a loop (where does it start/end?). But, in my setup, the audio interface's volume knob has no effect whatsoever on the volume of the noise. The studio monitor's volume knob DOES affect the volume of the noise however. As the studio monitor and audio interface are directly connected via a 1/4" cable, would this mean the noise is entering the signal between the two?

I would take after to mean later in the chain of signal flow. If you take your ears as the end of that chain and work back.......

When you say studio monitor's volume knob, is that a single volume controlling device, not in your OP, or is it the two knobs, one on each speaker?
In either case, the noise must be entering after your audio interface.
What kind of monitors are you using? Can you use a balanced cable from interface to monitor. Try one speaker first, then the other. It may help to lift the screen on the cables between interface and monitors.
DD

[Jakeman1086]

This is not to break from Whitlock's standard troubleshooting procedure, which I fully intend to follow through with, but I was discussing this issue with a more experienced person today and a few things came up. None of this is fact, but merely his hypothesis:

First, based on two of Whitlock's rules:

1. If the noise is unaffected by the setting of a volume control or selector, it must be entering the signal path after that control.
2. If the noise can be eliminated by turning the volume down or selecting another input, it must be entering the signal path before that control.

and taking into consideration the results of my tests:

1. turning the master volume of the Firebox audio interface down/up does not alter the volume of the noise.
2. turning the volume knob of the yamaha hs50m studio monitor down/up does result in a quieter/louder noise respectively.

we must conclude that the noise is entering the system between the resistor of the audio interface's master volume control (if it is indeed a resistor) and the resistor of the studio monitor's volume control (again, if it is indeed a resistor).

There is very little between these two components in my system. Here is my friend's hypothesis (to the best of my memory):

My new i7 desktop computer is operating at a higher frequency than my old dual-core. A voltage is being induced in the audio interface due to the computer, which is the noise I hear. This hypothesis seems to explain the symptoms I am experiencing:

Symptoms:

1.) The noise I hear is related to computer activity. It changes when I do something, such as open an application, etc. Some computer activities even cause the noise to disappear completely for a second or two.

2.) My electric guitar is recording the same noise. It is experiencing an induced voltage, as holding it near the computer makes for a very loud noise, while moving it further away or turning my guitar parallel to the ground (as opposed to perpendicular) reduces the noise greatly.

3.) It agrees with the location of where in the system the noise is being generated (in the audio interface after the resistor controlling the master volume).

4.) It explains how I can unplug every single cable in my entire system except for the power cord to my computer and the firewire cable from my computer to my audio interface (speakers also unplugged), and still record the noise from my preamps (with nothing plugged into the preamp!).

What do you think SAC/everyone else?

[SAC]

If the noise is induced, it will be most likely be in the (unshielded) wiring, not simply a 'resistor'. In fact, assuming the resistor is not a non inductive variant, the inductance of the resistor will actually resist ingress of HF noise to a degree.

And if the Case of the computer is not grounded (with reference to the computer wiring) to act as a Faraday cage against externally sourced RF and EMI????? Hmmm. ...And without knowing the computer manufacturer, why does the letter "D" flash in my mind?

Thus far you have 'concluded' that the problem is a ground loop and now apparently induced RF/EMI.

If the problem is induced noise, my gut feeling based on experience would lead me to check the interconnects and connectors first. And then the sound card and the Firebox as well.

And as mentioned before, the PreSonus Firebox has had pin 1 problems in the past. You might want to refer to Mary Gruschka's article on troubleshooting this issue. And also check the interconnects interfacing with that unit.

We can only speculate regarding the specific source of the problem based on broad past experience. But in any case, I would step through the comprehensive general procedures (which are NOT that difficult!) until the specific source was isolated to a particular stage. The Whitlock write-ups go into allot of detail explaining the whys and hows of the problem - don't let that put you off. The actual troubleshooting process is much briefer.
Alternatively, the Pin 1 troubleshooting procedure is pretty quick as well, and you might want to check the Firebox. (BTW, your use of a direct box is exactly what Bill Whitlock refers to when he speaks of the Iso-Max transformers - although the Iso-Max and Jensen transformers are some of the best, albeit at a price - various in line isolation transformers are available from a variety of MI and electrical supply houses.)

And as far as the CPU, it is shielded! That is the primary purpose of the metal case whose secondary function is heat dissipation. And computers are used for data acquisition every day. But the audio interfaces are rather infamous for the types of problems you are describing and THAT may also be a problem, as MANY have had MANY problems with noise ingress.
So, there are a number of possible causes based upon precedence. We can speculate forever, but ultimately the isolation process will work...if we actually try it.

[The Peschinator]

Here it is... invest in a BACP. This stands for "balanced alternating current power." All power in the mighty U.S. is unbalanced :( This is more or less the same technology that goes into balanced cables. There will be no need for any crazy fixes.

[SAC]

If the problem was noise on the AC line input, it would be present in a myriad places, not simply here.

And it would also assume that all of the power supplies were utterly inadequate.

[Jakeman1086]

The direct box I mentioned in my first post was before I knew anything about these issues. I am not looking for a band-aid fix, which I believe direct boxes serve as.

And I agree, speculation has done very little for me so far. I will start troubleshooting tomorrow. My friend (who knows a good deal about residential wiring) walked the property with me today. I have one ac neutral ground. I cannot identify whether the telephone ground is connected to the ac ground because what looks like the grounding cable for the telephone goes into a brick wall. He suggested getting a voltmeter (I think?) and measuring something (can't remember what right now) to verify the telephone and ac grounds are indeed one and the same. It is unlikely I can get AT&T out to check, but I can try (any good lies I can tell them?).

As for the troubleshooting process, how do I acquire the test adapter? Whitlock mentions:

The test adapters may be purchased from Jensen as ISO-MAX part numbers TAR1 for the audio RCA version or TA-R75 for the video RCA version. You may also build them and/or adapt them for use with other connector types as shown in Figure 4.

I will start testing at the speaker's (Yamaha hs50m) connection to the audio interface I assume. So, I will need a 1/4" test adapter to replace the 1/4" cable connecting the two. If this step doesn't identify the problem, I will go upstream to the connection between the audio interface and the computer. This will require a firewire test adapter. How do I acquire these two adapters?

[SAC]

In almost all of the Whitlock docs there is a parts list and simple schematic to make the troubleshooting test leads. For RCA connectors they are model TA-R1 and also available from Jensen Transformers for about $10 for a pair and a troubleshooting manual.

Starting on p13 of the Understanding Finding Eliminating Ground Loops in Audio & Video Systems and on p.5 of the Troubleshooting Guide there is a parts list and schematic.

Jensen Transformers, Inc.,
9304 Deering Ave., Chatsworth, CA 91311
Toll Free Order Line: 866.476.6291
end_of_the_skype_highlighting Voice:818.476.6291
WELCOME TO JENSEN TRANSFORMERS, INC.


As far as AT&T, simply call and tell them you need someone to check the ground. You don't have to make up a story! If they use a rod, insist it be common bonded. Its incombent upon them to verify the configuration.

As far as the procedure, follow the 10 page Troubleshooting Guide 'to the letter'! Its not difficult!

[naanod]

It looks like its been a few months since anyone has posted to this.

I happen to have almost exactly the same problem so I thought I'd contribute a bit.

For starters, It works perfect when I connect the audio interface into my macbook, same outlet, same surge protector---no noise! I really don't know what the deal is. I do a majority of my workflow on my PC so this is really a drag.

The only plausible solution I found in this thread was Jackman's band-aide treatment of plugging in the audio interface.

[jhbrandt]

Most of the time this is a 'loop-area' problem.

Try this:

bundle all the wires together - AC cables & audio cables so that there is no loop. use nylon ties. Just one big cable. Where the wires go into the monitors, tie the audio line to the AC cord so that it is only one 'cable' going to each monitor from the converter or monitor control box.

No stray cables or bundles are allowed.

See if the noise is reduced or eliminated. - Let me know!

Cheers,
John

[Jakeman1086]

jhbrandt, that sounds reasonable, but the problem is, this noise persists even when I reduce my setup to the following:

My desktop computer plugged into the power strip via an ac cable, and my firebox audio interface plugged into my desktop via a 6-pin firewire cable. When these two cables are the only cables in my setup, I still get the noise recorded through cubase when selecting either of the two preamp inputs to record.

I will be following Whitlock's troubleshooting procedure. SAC, I will be using this test adapter for a TRS-to-TRS connection. Can I just buy the TA-R1 (for RCA cables) and buy two RCA-to-TRS adapters to stick on the ends?

[SAC]

For balanced lines/connections, follow the Gruschka "How To Test For Pin 1 Problems" procedure. How to Test for the Pin-1 Problem, by Mary C. Gruszka

This can be easily made with a standard wall-wart transformer and an appropriate light socket. Just verify the ratings.

I think I may have neglected to provide the link to this 2nd of the 3 excellent Mary Gruschka articles regarding Pin ! troubleshooting. (oops!) (Since fixed) This will specifically help with the balanced line troubleshooting!

----------------------------------------------

The rest are simply a few additional aspects noting that problems can originate in one place and become apparent in another!

"Barring fixing the equipment itself, take care in cable interconnection. Find a way to connect the shield of the signal cable to the equipment chassis instead of through the connector. This means breaking out the shield from the cable connector and finding a convenient place on the chassis, ideally near the mating connector, for a chassis connection. You may need to scrape paint and add a toothed washer beneath a screw to get a solid connection." Gruschka. Resolving Pin 1 Problems (but FOLLOW the procedure step by step! Do NOT use this out of context!!!!)

Oh, and if folks are using XLR connectors, I cannot recommend the Neutrik EMC-XLR - NC3FXX-EMC series enough that feature the addition of an annular capacitor to avoid the issues related to the pin 1 issue.

Oh...and I may as well mention to verify the integrity of the video paths as well, which can definitely cause audio issue as well.

"This brings up the point that pin-1 problems may not always manifest themselves at audio frequencies. If the shield is connected to the chassis by a small length of wire or trace, it may act as an antenna at RF frequencies, but not cause problems in the audio range. Also, pin-1 problems could cause the internal clock or other types of noise to be radiated outside the chassis and be a potential source of interference to other pieces of gear. This can easily snowball.

I've used analog-balanced interconnections for the examples presented here, but pin-1 problems can lurk in unbalanced inputs and outputs, as well as in digital equipment.

Although induced noise may not be heard directly in digital equipment with pin-1 problems, that noise could be enough to prevent the digital signal from being received/decoded properly somewhere else in the signal chain."

[Jakeman1086]

Okay, SAC. I want to really reduce this to the bare-bones, because I am not an electrical engineer and am very lost (not your fault, I get easily confused).

I reduced my system to my desktop plugged into an ac outlet and the Firebox plugged into my desktop via a 6-pin firewire cable. Beyond the wall's ac outlet, that's it! Absolutely nothing else plugged in anywhere. The noise still gets recorded in cubase when I select the audio interface's preamps as the source to record (and even with nothing plugged into these preamps).

Thus, if the noise is not an issue with my house's grounding in general, wouldn't the problem HAVE to come from:

a.) the computer itself
b.) the firebox itself
c.) the firewire connection between the computer and firebox?

I mean, there's nothing else in the system.

Since the firewire cable is not balanced (correct me if I'm wrong), pin-1 problems would not apply. What do I do?

[SAC]

Are you using a microphone? My guess is that you are getting the signal into the mic pre-amp somehow...

They (mics) are CLASSIC sources of pin 1 problems.

Also, out of curiosity, do you have a 2nd computer, or access to one via a friend, etc., that you could swap for testing?

[Jakeman1086]

No, a mic is not plugged in to get the noise. No cable, nothing. The only cable going into my interface during the recording is the 6-pin firewire cable.

I have another desktop computer. It is my old one, a dual-core, which I replaced with the new i7. And if I plug the audio interface into the old computer, the noise does not exist. So, obviously the new computer is related to the problem in some way.

What does this indicate?