I am certainly no authority, but could this be caused by the infamous ground loop hum? If so, search for that topic at forums main page, there is a thread with answers. The solutions offered worked for us for ground loop hum. Cheers.
Monster HTM 3500 conditioner is noisy
I just purchased and installed the above equipment based on all the rave reviews, namely at TAS. I find it amazing that a component which is designed to reduce background noise actually emits a continual buzzing sound when turned on. I wonder if my unit is defective ? A unit designed to shave a couple of dbs from the background noise should be ultra silent! My listening position is relatively near where the equipment is located, and no other piece is at all audible, while this component is. Anyone had any similar experience ?