Update: I've decided to revamp my system. Replacing Denon AVR 2803 with a B&K AVR 507. May take Adcom GFA 7000 completely out of the equation. Hoping ground loop problem will resolve itself following changes.
Musicnoise: Thank you for your extensive explanation. Thanks again to all. I learned a lot from the process. Will be back on this thread if unable to resolve problem if it persists.
Musicnoise: Thank you for your extensive explanation. Thanks again to all. I learned a lot from the process. Will be back on this thread if unable to resolve problem if it persists.

