Great. This means the problem is likely a noisy transistor in the output stage. I am at home today and my receiver is at work, so I can't look at it, but from memory the output stage is a separate board located at the heat sink, about the middle of the receiver.
Buy a can of freeze spray and connect a pair of speakers you don't care about. Spray a very small amount of freeze spray on each transistor on the amp boared, one at a time and wait about a minute between each. Try to get the freeze spray only on one transistor at a time with no overshoot to other parts, just press gently on the trigger. When you find a transistor that makes the noise get worse or better when you shoot it, that's the bad one. It's going to be one of the small, black plastic ones.
