I found a couple of posts related to but not exactly describing this problem I am experiencing with my home studio setup (196682-my-gear-electrocutes-me).

I will try to be quite complete in my description to avoid the need for too much clarification. Sorry if this turns into an essay!

First and most important, electric shocks.

When I run my asus laptop on battery (because of the godawful noise the psu introduces into recordings), my Edirol FA-66 firewire interface becomes 'live' to touch. On the corners (I guess where the surface is smaller) this becomes more unpleasant and makes connecting anything impossible. With laptop on mains this doesnt happen. I also had a similar problem with rca connectors from a hi-fi amp, and one of my mixers had two channels fail (I'm sure due to being connected to these rca cables). An even more extreme instance occurred when recording a Mesa valve head. Even when not directly connected to my mixer through DI, the mixer's metal surface became VERY live when the amp was switched on. No ground lift on the amp or anything, and it had a 3-prong plug.

Second and ultra important, noise.

As I mentioned above, attempting to record from line in or mic in with the laptop plugged in results in a high-pitched whiny machine noise which picks up scrolling and changes in screen etc I also experienced this, as did others, at a regular laptop performance night I was doing in a medium-sized venue. The solution for everyone was always to run the laptop on battery power, which made the noise completely disappear. However, even with battery power, the guitar is still susceptible to a mixture of buzzing, hum and monitor interference. I gave up on using my rackmount effects units in the pedal chain as they just seem to amplify the noise to ridiculous levels.

I also have a dimmer switch in the bathroom (right below my bedroom/studio), which obviously needs to go, as it makes a horrible buzz anytime someone swicthes it on and I have either my Roland Cube or Traynor valve guitar amps on. Would it be a simple matter to just bypass the dimmer circuit but keep the switch mechanism? It's a tiny pcb-type thing. The light fixture is a pull-switch, and the only one I found which doesnt make a ridiculous mechanical 'ker-ching!' sound is the silent version with dimmer switch (not so silent through the mains though!)

All my equipment is running from a single wall socket, to a belkin powerstrip, and then to various other 4-gang power strips from there. Up to 24 plugs in total, and several (what I'm guessing are) 'switchmode' psu's for external hard drives, the FA-66, Roland Cube, hard drives, laptop etc. Monitoring is through headphones or a hi-fi which register the noise equally. Worth also noting is that the belkin makes a quiet fizzing sound constantly. I have a switchable voltage psu for a footswitch that also makes a louder version of this sound.

My intuition says there is something wrong with the electricity supply..? I have a multimeter but found an article on the net that strongly advised against testing mains with one.

As much of what I do involves guitar through a valve amp, all these problems make for a VERY noisy signal and worries about the health of myself and my gear. My laptop screen, even with a guitar that has humbuckers, creates noise. The valve amp also seems to pick up random buzzes which come and go, unrelated to the bathroom dimmer switch. I have also tried unplugging the fridge to no avail. I have no fluorescent lighting anywhere in the flat. I am living in a maisonette, and so its possible that items in the flat below are sharing the same wiring.

Is there a possible solution to shielding my valve amp from stuff like hairdriers, washing machines etc that may be polluting the electricity supply with noise?

But more importantly what to do about these electric shocks and live surfaces of my equipment?!

Mate, I cannot for the life of me understand why you have not called an electrician in to look at the potentially lethal electrical issues you have instead of posting about them here! Sorry - can't offer any other advice but do not touch or power up the gear until you get a qualified electrician to check it all out and isolate the fault.....

I got one of those electrical socket testing devices, and all my sockets and powerstrips tested as being safe.

After speaking with an electrical engineer, I was told what I probably have is a ground loop somewhere. He also advised the following:

Get a sinewave UPS (for around £1000!). This would clean the power supply and isolate it from noise, mainly a solution for recording clean tube amp sounds though he said this may also cure the shock problem. Wood Green area apparently suffers from quite a 'dirty' electricity supply. Unfortunately for me the UPS too expensive, and these units make a LOT of noise acoustically so it would need to be housed in some special enclosure etc, basically too much hassle and money for me right now!

Another suggestion was to plug the laptop in to a power strip with an off switch when running it on battery power, to earth it. I will try this and post my results.

Another possibility suggested is to add ferrite cores to audio cables currently I have these fitted as standard on firewire and power cables for Edirol FA-66. The laptop power cord and hard drives also have these.

The basic prognosis was that probably one or more piece of gear is faulty and it is not the house wiring that is causing this.

However, I wonder how accurate these consumer mains testing devices are, and why both noise and shock problems seem to fluctuate in intensity.

Thanks for the concern and advice to get a sparky. I am very dubious about a regular electrician doing much more than charging a load of money just to turn up and do the same mains test I have already done!

I'm open to suggestions though!

this is the crux of your problem.
ouch!

You haven't recently had any equipment modded have you?

Hm, I was under the impression that running every extension socket from one single point was the recommended practice for avoiding ground loop hum. Or is this only for venues? Could you explain why that would cause the problem, and if running say 10 plugs of 1 socket and 10 off another would make a difference?

No equipment modded in any way.

Important update to this post..

In case anyone runs into similar issues in future!

I eventually identified the problem as being a pc laptop (which used to be my daw, and thus never got removed from the equation until I got a macbook pro, thank god!)

The crappy switchmode psu was leaking current into anything and everything that had a metal surface, including jack sockets. It eventually fried a couple of channels on the mixer I had. Matters got quite scary when I was tracking with a Mesa F50 amp which drew a lot more current.

I'm still running everything that is inter-connected (guitar amps excluded as they are being miced) to one surge protector, which each extension cord is plugged into. As far as I know, the 'star configuration' from one socket is the best way to keep ground loop issues to a minumum.