If the sound is from the amp itself and not through the speakers, its likely a transformer vibration which I call buzz. Try telling your dealer its a transformer buzz and ask them to tighten the hold down bolts. These are sometimes difficult to prevent, but if you bought it from a retail dealer he should help you out.
If the sound is through the speakers it may well be a grounding issue, but since you say you have an HT processor, it may be your cable TV. Try disconnecting the cable co-ax and see if it goes away. If it does, try a ground isolation transformer which can be purchased at radio shack.
If the sound is through the speakers it may well be a grounding issue, but since you say you have an HT processor, it may be your cable TV. Try disconnecting the cable co-ax and see if it goes away. If it does, try a ground isolation transformer which can be purchased at radio shack.