Newbee (time to change your name, dude) is most likely right. In addition to poor ground at outlet, could also be a bad IC ground, or induced hum from an IC or speaker cable near the power cord.
Hum or buzz through speakers
I just turned over my system from all B&K to Audio research and McCormack. I was running the Audio Research through the B&K until Monday when I put the McCormack DNA-1 in place. I am hearing a hum or buzz through my Vandersteen's audible from three feet away. Preamp is ARC SP9MK2. Tubes are 6922 Golden Dragons which I am going to change over to some Amperex 7308 USN-CEP. Would this be tube noise that perhaps the McCormack is picking up where the B&K did not or is there something in the McCormack amp that would cause this.
Eagleman
Eagleman