Try cheater plugs to lift the grounds on various components until you find the mismatch and leave it there.
How to get rid of groud loop noise from dish ?
I just bought a sony 9000 DVD player, but when I connect the component connecters to my tv I get ground hum in my stereo system. I tried filters on the incoming coax, but the signal from direct tv will not pass through it(it did get rid of the hum). Does anyone have any suggestions?