When the gpu stopped processing sigificant content in XP, the noise went away). I could tell that the noise was associated with the gpu because the frequency of the noise was always in synch with what was being displayed on the screen (screen scene change resulted in a change of noise frequency. It didn't matter if the monitor was on or not, only that it was plugged in (but it was worse when it was turned on). It only happened when the monitor was plugged in to the gpu and only if it was plugged into the mini-display port. It is the result of electronic noise leaking from the monitor into the gpu and thus into the computer system. Through the process of testing i discovered it was interference coming from a second monitor on XP via the GPU. I have noticed this a little once on my system.