Buzz/hum from amps, NOT from speakers

I have been tearing my hair out over over a buzzing noise coming from almost every component in my system. I have it in all three subwoofers, the power amp, preamp, and - the latest addition - my new HP plasma TV. All will "buzz" quietly as soon as they are plugged in.

Using a power console makes no difference, and I've tried both a Monster Power 3500 MK2 as well as a Belkin PureAV PF-60 (both are ~$500 units). I've tried the ground-plug "lifters" that turn a 3-prong AC plug into a 2-prong, same problem, no change. Removing the audio interconnects makes ZERO difference. The noise is present with ONLY the AC cords attached. I tried shutting off EVERY breaker in the panel box except the one that feeds my system, no change. I have tried different circuits, no change.

Sunfire mentions this in the owner's manual, which sounds like what I'm dealing with, but they offer no solution:

"If the hum is heard from within the
TGIV and not through the speakers,
this may also be caused by
interference on the AC or DC lines.
The power transformers may turn
this interference into an audible
noise. Internal hum can be made
worse by a shelf or cabinet resonating,
so try moving the TGIV to another shelf."

Equipment affected:
====================
Sunfire TG IV preamp
Sunfire Signature power amp
Sunfire Signature subwoofer
Polk SRT main powered subs (L&R)
HP PL5060N plasma TV

HELP!!!!

:-(