These coils are absolutely wonderful for picking-up all and any electromagnetic radiation, this is what they do best, it's how they work.
Do not play near any transformers, electric motors, fluorescent lighting (incl the new energy-saver bulbs), anything spitting out RF. The computer is probably creating an eddy current in its case. Shielding is futile, it can act as an aerial.
Short of re-designing the computer to break the dielectric coupling betwixt motors, transformers and chassis, there's not much that can be done. Move away, the inverse-square law applies (if it is 1 at 1d then it is 1/4 at 2d and 1/9 at 3d...). However most guitar amps will benefit by raising the transformers off the chassis on a sheet of Paxolin (PCB), the bolts still keep the frames earthed. Better still use an aluminium chassis.
There's two kinds of people, those that hear the music and those that don't.