Note: 5 year old thread was resurrected by a new member today.
So the problem is likely solved by now.
I am guessing as well that this was resolved oh, years ago.
BUT- most interior audio cabling ain’t exactly well-shielded. If your audio cables are laying against / crossing the power cables but not exactly at 90º, you can get wicked hum or “thrumming”.
Always good to look into that as a culprit.