Has to be radio transmission. Taxis and other FM transmissions can come across like that. i.e. conversation length bursts of 'white' noise.
If they are on your monitors they must be pretty strong. Try recording them. Say a mic cable into your pre, no mic, high gain.
There are also software oscilloscopes which might visually show the bursts.
What to do about it is another matter. You might try RF suppressing mains leads. These are not the spike arrestors which are sold to protect computers and such. RF suppression would have ferrite magnetic attachments. Mains Filters - part 2 - Ferrites and VDRs
Impossible for me to be sure, this is just guessing.
Input volume off and nothing on the recording seems to suggest that the RF is being carried on the mains wiring. It may not be specifically radio either, could be something computerish I suppose. But in any case, those Ferrite blockers are what is used. e.g. Mic pres often have small ferrite rings at the input.
Depending on your knowledge and skill set, you could try to test the quality of your grounding. I don't know your codes there but I have lived in California. I can tell you the standard of wiring installation here and in England is way superior. Has to be with the lethal voltages. Voltage aside, there are stingent grounding requirements. Also grounding is sometimes done in enhanced ways in audio situations. I would try to find an audio savvy electrician.
EDIT, I would try the recording idea again. This time insert a length of bare wire into one of the terminals on the XLR. This will act sort of like an antenna but it might defeat the CMMR (noise rejection) of your pre.
Even a straightened out paper clip might do. Place this next to the mains cable of your amp. If we could get a visible waveform it might provide a clue.
However, I would start ordering some ferrite or even an isolating transformer with enhance RF filtering.
Neither of us will understand until we nail this sucker...!
Are you comparing like with like?
i.e. Do you have these domestic items in your studio, or have you tried your amp in the TV room.
The other thing that comes to mind is that both your amp and monitors (presumed active) invite input while your other gear is self contained.
Again presuming your monitors are active, remove the input cables and let's see if the noise continues. If they are not active remove the input cabling from the amp driving them. Similarly remove the input (guitar) cable from the amp.
Even with the level down or off these input cables could act as antennae or the gain control could be post the first amp stage.
Thanks for the idea, I'll try that a little later.
Just to help me understand- if the noise was coming from the mains wiring, wouldn't I also hear it from the tv, stereo, radio... somewhere else?
Not necessarily, sometimes things are real strange when it comes to these things.
I have seen 60Hz transmissions from faulty grounds that we could trace all the way back to the electrical pole across the street (underground service in that case) using a Fender Mustang with a portable amp (took us a long while to solve that one.) That particular problem was only affecting single coil pickups.
I have seen where 1 amp (out of 1/2 a dozen or more) was a radio transmitter for a particular radio station.......
Sometimes the sources for these problems are very VERY hard to pinpoint. (The ground issue took us 3 months to figure out - less than an hour or so to fix once we did figure it out.)
I stuck a paperclip in the XLR input and was able to record the noise.
I plugged my Apogee Jam into my iPad, and recorded my guitar direct. NO NOISE! Even tho the Vox amp a few feet away was buzzing the whole time. This is while sitting right in front of my monitors, computer, power amp, etc etc.
This seems to rule out any airborne interference? Which means the noise must be in the wiring?
Thanks so much to both of you for taking the time to help me with this!
Noise will probably travel much better through wire than through air.
However, a wire carrying noise currents is an antenna.
So, try moving your paper clip mic cable noise sniffer device directly next to mains cabling. Record the loudest sample of the noise that you can catch and post a few seconds of it here. It may have a visible or audible clue.
Continue to test individual non connected items, e.g. Mackie alone. Guitar into DI into Mackie.
And so on, I think you have the concept well in mind now so good luck with the search.
Here's a sample, recorded with a paperclip stuck in the XLR in, with a wire wrapped around it and draped over the Mackie's mains cable.
My interface is a Focusrite Saffire, all other inputs and outputs were disconnected. The Saffire is powered by the firewire buss, I had headphones plugged into it also, no other devices plugged into the Saffire.
Hope this helps. While recording this, I noticed that the noise was not happening as often, or lasting as long, as earlier today. Another piece of the puzzle, perhaps.
Hmmm, doesn't sound very radio does it? But let's not rule that out yet.
Was the Samson On while this recording happened. Modern amps use all sorts of tricks to avoid having to have an expensive transformer to do the heavy lifting. Let's see if the noise goes away with the Samson off. Then continue to turn as many things off as you possibly can.
Does the noise appear in the Mackie Headphone out?
Could be the Saffire or the Computer or some interaction between them.
Can you power the Saffire off an external wall wart?
I think the noise comes thru the Mackie phone out, I'll confirm that later.
I can power the Saffire from a wall wart and see if anything changes.
I'm thinking tho: since I get the noise in other rooms, the culprit isn't necessarily even in my studio, it could be anywhere in the house, or coming in thru the mains? Rather a depressing thought, I'd say.
I'll try disconnecting everything I can and see if I can narrow it down some.
It doesn't seem like either of those would be so consistent time-wise. But I'm not ruling anything out. Later today I'll turn off the breakers to the heating system and water pump and see if I learn anything.
Off the top of my head - I cannot think of anything that would cycle in roughly 2 minute increments.
Good systematic approach, Rod. That's what these problems require.
OP: It is worth observing it over time to see if the 2 minute period is constant or not. Assuming that the single coil pickup is the only receiver that is hearing the noise source in the studio chain, have you cranked the amp and walked around with the guitar to see if position or orientation make a difference? If you can get your hands on an osciloscope, you could look at the stability of the A/C in your home and see if it shows any noise on the incoming A/C at the time you are hearing the noise through the amp. Do you know if there are any municipal facilities in the area? I have seen sewage sumps that run on regular intervals and they can produce huge RF noise because their motor windings are so large. We had to place a Faraday cage around an entire laboratory because of an adjacent sewage lift, even though it was buried 20' underground.
Good systematic approach, Rod. That's what these problems require.
These problems are not always easy to solve - this because they are not always easy to find.
I mentioned earlier it taking 3 months to solve a noise problem like this before.
We identified it early on as a 60Hz signal - the facility is in the US - so we knew it was related to the power company in some way shape or manner.... still took us 3 months.
In the end the problem was caused by a water pipe.
The building we constructed had 2 corridors that connected to an existing building sitting between it and the road.
The existing building - new building - and studio all had their own power. There were no interconnections in those power systems.
However - it made no sense whatsoever for us to develop new domestic water service to the new building when the existing building already had more than enough capacity - and the volume of water between the 2 buildings would not exceed minimum usage they were already paying for.
So we tied into the existing building services and brought the water for the new building through one of the corridors connecting the 2.
When all was said and done - that interconnection cause an issue with the same water system having multiple points to ground - which caused the loop.
3 months to figure it out - 1 hour of so to install the dielectric union breaking the loop, which then solved the problem.
Rod: I have a battery powered amp, it does make the noise when running on it's wall wart. I'll have to get batteries today to try it that way. Unfornately, we're in the middle of a blizzard right now in NH, so I won't be getting out of the house for a few hours.
I like your logical & systematic approach tho, and will follow those steps.
Sync: I'll keep the stopwatch on it at different times during the day, somehow the timing seems like a good clue. The noise seems unchanged by position of the guitar or amp, even room to room.
I'm in a pretty rural area, no industrial/power/municipal facilities nearby.
I can imagine it's pretty bad up there - It's bad down here in CT as well....
How far are you from Portsmouth? Curious because I just did some work at the Pease Army Reserve Center there.
Rural areas still have transformers - just they are smaller in nature and usually are mounted on the telephone poles......
The timing you mentioned earlier is a little screwy from my perspective - things like heating systems, water pumps, refrigerator pumps, etc., should not be running short cycles like that - in fact I can't think of anything that should be off the top of my head.
Best of luck to you with this - be sure to keep us posted.
I'm about an hour from Portsmouth, which I think today is a good thing- looks like they're getting pounded pretty good.
I keep looking at my cell phone, thinking that's a transmitter. But I've shut it off, even taken the battery out, and nothing changes.
I have the stop watch on it now the timing is not so consistent. The noise has stayed on for more than a minute at one point. But I can't think of anything that's going on in the house to cause the change.
Anything with a large motor is suspect. Since the noise does not change as you move the guitar around, I don't think it's airborne. So heater, fridge, etc., if it's in your home. If it's outside your home, then you'll have to look at isolation.