hum, please, please help

I have a hum issue that I am starting to troubleshoot but need some help on what I can eliminate as the problem. If I plug all components in normally to the dedicated 20 amp lines I get a hum. If I use cheater plugs I still get a hum but it is quieter and somewhat tolerable but audible. If I crank up the preamp the hum gets a little louder. I know that dimmers can cause this problem. I have no dimmers in my dedicated music room but in the next room I have a dimmer switch for recessed lighting. So I decided to turn it on and turn up and down the brightness of the lights and this definately affected the hum. If I turned it way up it got a little louder and got more quiet as I lowered it and when I turned it off the hum stayed like it was before. So my question is if this dimmer is affecting the hum or contributing to the hum is this a ground loop issue or a grounding issue or an electrical issue? My equipment consists of Escalante Fremonts clayton audio m-300 monoblocks, hovland hp-200 preamp and amr cd77 for cd player. I also tried running a ground wire from my preamp to one of my amps and this did nothing. Any help would be very aprreciated.