Grounding seems highly unlikely to me as the source of the problem, as HD clicks and such shouldn't be affecting the earth ground through the computer power supply, which is VERY well isolated for obvious reasons.

I trust you have visited the sounds dialog in control panel and chosen "none" for the sound scheme option, and turned all "system sounds" OFF ?

I suppose you could confirm the ground problem by plugging the soundcard power into a seperate house circuit using a long extension cord if necessary, and checking if the problem persists. Sure seems to me that this would have to be happening on the downstream side of the CPU power supply though. Like the computer equivalent of poor channel isolation in a preamp... ?

And yes, I imagine that a maxed CPU would generate this kind of problem as well... have you watched the system performance monitor while performing parallel tasks that tend to cause this problem?