I had a similar problem regarding hum with my setup. I went from a dead quiet house to a problem when I moved here to Arizona with the left speaker humming. My speakers have amps in them. When I talked to Richard Vandersteen, he advised me to run a ground wire from the humming speaker amp to the main amp or preamp which quieted the problem. It seems that the speakers were on a different circuit than the other electronics which created the different ground potential. Try running a very thin wire touching different components and see if it works. In any case, using a cheater will ruin the sound..grainy, no depth, etc.
Quality Cheater plug??
I have a hum in my 5 channel amp through the speakers and when I disable the ground prong on the power plug it is dead quiet. I am looking for a good quality cheater plug that would be used with a Cardas GR Power cable. I would rather find the hum but this is the second amp that has done this same issue. Any help would be appreciated.