I agree those would all be potential sources of trouble. I have my entire system on a single 20A dedicated circuit. The only thing plugged into the 20A circuit is my Brickwall 20A surge protector which has 10 outlets arranged in 5 "isolated" banks of 2. My amp, prepro, tv, dvd player, and sat dvr are plugged into the Brickwall. I've mixed around the various devices into different outlets on the brickwall to minimize the hum but it doesn't go away. And all the wiring is copper. This is a very new house hence it has no aluminum wiring.

Maybe an audio power specialist could help me but I kinda doubt calling an ordinary electrician would help. I wouldn't let any electrician I've ever met even touch my AV system!

Thanks for all the ideas AvFan! I'll keep working on it . . .