Loud Hum

Thank you for all your responses. I have one basic question. THe hum is there even when the lights are out. Could this be caused by the dimmer even if the lights are out? Also, when I disconnect the interconnects from the pre amp the hum is gone (mostly). Could it be the cables I am using?
The B15 actually is on a "cheater" (no ground) but it still has the "Hum". I am not sure (and honestly I doubt) that the electrician that installed the dedicated power lines for the amps also used a separate ground. I will do this if it is necessary. The worst hum is coming from the proceed running the surrounds and center (this amp is not connected to a dedicated power line).

My 7BST's have a ground loop switch on the rear panel. If your amps have this just flick the switch.

Dynasys- No, if you turn off the lights, and the hum remains, it's a ground loop problem. Good thing; you don't have to listen in the dark! You don't need a separate ground for the wiring. In my system, I had a terrible time getting rid of the hum. My Plinius pre-amp had no ground switch (internal cheater?) which helped a little. Eventually I had to put a cheater on everything but the preamp ( I plugged everything into a PSAudio plugstrip,except the power amp. I put a cheater on the plug strip. I still had the hum. I unplugged the cable. Less hum. I put a cheater on the power amp. The hum went away...) I also bought a coax ground cheater to divorce the cable from the ground (you can get the mondial magic isolator from audioadvisor.com for 100 bucks.

I had a similar problem. I solved it by installing dedicated 20 amp circuits.
You've got a lot of amplifiers drawing juice and when they don't get the juice they want, the transformer hums. Not exactly sure why -- I'm a layman when it comes to the technical side and I cannot recall the explanation I was given.
Everything in my system with a transformer, amplifiers, sub-woofer, and even
AC Conditioner was humming. But, when I installed the dedicated 20 amp circuits, all humming stopped. System is quiet as a stone.

I once had a problem with hum. It was caused by Halogen lite bulbs. I asked a few of my knowlegable friends how to get rid of the hum but nothing worked.Since it only buzzed when the lites were on, I thought why not go to regular bulbs. Presto, no more hum. My friends were impressed.
Do you have any halogens in the room or nearby?