Turns out I had a dual problem. Primary one was cable TV ground problem. Tried to resolve it by rewiring the cable box, but the morons have grounds to the electrical system, gas pipes, etc. Ended up buying an inline device by a company called Viewsonics from a local audiophile store for $30. Their Web site is www.viewsonics.com, though I didn't see this filter listed. The other problem is was sort of mismatch between the amp and preamp. In addition to calling the pre's manufacturer (still waiting for a call back) I floated the ground on the pre and the noise floor is vastly quieter. Finding the problem, as Bob said, involves starting at one end of the system and working back to the other end.
Audible Hum
I just hooked up a pair of Clayton M70 monoblocks to my Martin Logan Requests. There is now an audible hum coming from the speakers when the volume is off. The amps are located close to the speakers.Is this the problem? I am new at this and would like the groups help. I did not have this problem with my B&K amp which I replaced.