Check the A/c plug on the back of our amp...if there's a 3rd prong on the unit, that is more than likely the cause of your problem. The extra conector will generate a 60 hz cyle humm which may be coming through you cable TV...try disconnecting your cable vision and see if the problem does away. I had the same problem and the culprit was my cable which was not properly grounded. Unfortunately, the only workaround was to buy a cheater plug (which as I understand can be a fire hazard), OR purchase a Jenson transformer ground loop isolater. I picked one up off Ebay a few months ago for 50 dollars and the problem was solved immediately. Here is the part # VRD-1FF and here is the website to lern more about the product http://www.jensen-transformers.com/
Good luck
Good luck