For the past couple of weeks, I've been noticing there's a high frequency tone, like 10-12kHz or so, coming out of my G5 dual 2.0GHz (2nd generation model). Acoustically, it's very faint, but the problem is that it is coming through the electric guitar pickups, and also through the microphones (RE20 & M160 so far) no matter where they are placed in the room! I have no clue as to what is causing the problem - it sure isn't getting into my recording signal path acoustically as those highly directional mics seem to have zero influence in taming this tone (distance seem to have no effect on the volume, either). It sounds like pure sine wave, like from a tone generator. The tone is not constant, it comes and goes randomly, doesn't seem to have any relations to specific actions/operations.
I have tried removing the super drive as well as the recently added internal hard disk just to see if any of those mechanical parts are causing it, but that didn't help at all. Would anyone know what maybe the problem? Is there a certain angle which I could give a Karate chop at to shut it up? Thanks for your help!