Brian,
This is very simple and seems stupid in light of all the technically great suggestions, BUT...I had an Edge amp and never got any noise (hum) in my system. Bought a nice Nuforce Ref 9 V3 SE mono pair and all of a sudden I had a hum in my system like you described. I had an extra Maestro outlet sitting around and I ran a line to it from my panel. Plugged the amps into it and no more hum. My house is about 12 years old. I've since installed Maestros to replace the needed outlets near my equipment. Been a year and a half since and still all is fine.
This is very simple and seems stupid in light of all the technically great suggestions, BUT...I had an Edge amp and never got any noise (hum) in my system. Bought a nice Nuforce Ref 9 V3 SE mono pair and all of a sudden I had a hum in my system like you described. I had an extra Maestro outlet sitting around and I ran a line to it from my panel. Plugged the amps into it and no more hum. My house is about 12 years old. I've since installed Maestros to replace the needed outlets near my equipment. Been a year and a half since and still all is fine.