I have the same problem with my audio system. My MonsterPower HTS3500 hums when I turn the lights(dimmer) on. I also get the hum when I turn on my pre-amp. I am pulling my hair out trying to find a solution to the problem. The only thing I can think of is the kitchen (with flourescent lighting) is nearby, and this is causing a hum in the AC line. You might try moving the amp to another room to see if you still hear the hum. A power conditioner may help, but as you can see in my case I have a similar problem even with the conditioner.
Amp "Hum" caused by dimmer switches
I just recently got an Acurus 100x3 amp to drive the front 3 speakers of my home theater system and I am disapointed to find out that my room light dimmer switch is causing a very noticeable "hum" that can be heard from the listening position when no audio signal/ low passages are present. I did not have this problem using the amp in my harmon/kardon receiver. I do not want to remove the dimmer and go to an on/off switch and do not have the money for a power conditioner. Am I out of luck and have to resell the amp? I bought it used from this sight so I can not return it. The amp sounds very nice when the lights are not in use. I'd love to get some sound advice! Thanks!