Q:

Electrical noise on guitar pickups from computer. Due to radio interference, or inductive coupling?

When I point my guitar pickups towards my desktop computer from several feet (2 1/2 - 3) away, I can hear a lot of buzzing/clicking, depending on what the computer is doing (idling vs, say, playing video). Are the pickups picking up radio interference from the computer which is being demodulated by the amplifier, or are they inductively coupled to the computer, despite the lack of coils & distance?
I have trouble believing that it's radio interference that they're detecting (I've never gotten an AM signal through my amp, for example), but given the distance, I also have trouble believing that inductance is generating the noise. Can anyone shed some light on this?
Thanks
EDIT: To clarify, I'm talking about a single coil pickup, not a humbucker. I'm not really interested in reducing noise, it's not an issue for me. I'm just curious about what mechanism is involved.

A:

There is probably some of both going on.  A vibrating guitar string causes only a small voltage to be produced in a pickup coil, so the output of these have to amplified quite a lot.  Due to the high gain, small amounts of noise that would otherwise go unnoticed become audible.
One way to tell the difference between magnetic and capacitive pickup of the noise is to shield the pickup electrically but not magnetically (or vice versa, but that's harder to do).  If the pickup is already in a metal case, ground that case to the ground of the amplifier the pickup is connected to.  That should significantly reduce capacitive pickup but not change inductive pickup.  If the noise is still there, then it's not from capacitive pickup at the coil.  That doesn't necessarily mean it's due inductive pickup by the coil since there are various other paths of noise into the system, but you've eliminated one possibility.

A:

You can shed a little bit of light on this by playing with the guitar (i.e. pickup) orientation. If some orientations are much noisier than others, then almost certainly it's the inductive coupling.
As to whether the interference is in the RF region and your amp is rectifying it, my guess would be no, but if you really want to be sure, try adding a small cap in parallel to the input of your amp, something like 100 pF (which will slightly affect the tone). If that gets rid of most of the noise, then it was indeed RF.

