I think ALL components would need to be grounded to the same Lug as a Ground Loop is caused by components using seperate ground paths and the Amp is plugged into it's own wall plug; is this plug on the same circut as the one the rest of your components are plugged into? Here is a little background info on Ground Loops:


Ground loop is a condition where an unintended connection to ground is made through an interfering electrical conductor. Generally ground loop connection exists when an electrical system is connected through more than one way to the electrical ground.

When two or more devices are connected to a common ground through different paths, a ground loop occurs. Currents flow through these multiple paths and develop voltages which can cause damage, noise or 50Hz/60Hz hum in audio or video equipment. To prevent ground loops, all signal grounds need to go to one common point and when two grounding points cannot be avoided, one side must isolate the signal and grounds from the other.