Buzz/hum caused by new a electric lines

On Thursday I decided to run dedicated 10 gauge lines on 20 amp breakers for each amp (Joule Rite of Passage)and a separate line for the front end (Jadis preamp). Well, everything seemed to be fine except for a buzz/hum in the right speaker. I searched for most of the usual suspects accompanying electrical noise. First thing I did was remove all interconnects from the preamp. Hum was still there. I muted the preamp and found a very quiet buzz from the amps alone. Only audible if I stick my head into the speaker. I tried switching the left and right interconnects from amp to pre. The buzz moved to the left speaker. I thought it may be a ground issue, so I dropped all grounds. No change. I tried different ic's. No change. I plugged preamp into a completely different set of outlets with different power cord. Buzz persisted. Swapped all cords with no success.

One thing I did notice was that as I turned the left amp off (variac controls power)the buzz decreased by nearly half. These amps/system were very quiet prior to the wire change. What could I possibly have done? I am still unable to determine if the buzz originates in the amps or preamp or a combination. Just so odd it should be isolated to one channel. One other thing I tried was physically moving and switching the amps and found the buzz stayed on the right side.

Any help you can offer would be greatly appreciated. The buzz goes somewhat unnoticed when the music is on, but in between cuts it is quite annoying.