Do you have cable TV in your system too? That can often cause a ground loop through the coax cable. Try getting some "cheater plugs", one for each three-prong plug in the system, and use them in various combinations. Always have at least one component (preferably the amp) grounded though, for safety. This worked for me before--I used a cheater on my preamp and left my amp grounded and that killed the hum. Good quality power conditioning may help a lot, too.
Grounding problems-- Help!
I just bought a McCormack DNA 1. I am using the creek OBH-12 passive device as a preamp and my source is a Rega Planet. My speakers are ML areius i's. I hooked it all up and I'm getting a nice hum at 60hz. Please give me tips/ suggestion. I don't know anything about grounding problems!