preamp-poweramp hiss (loud)

I used to have a PAT4 & it was rather noisy. Can't explain what's happening re: your balance control affecting that though? I did replace all the stock resistors with low noise metal films of identical values, which helped alot.

Try hooking units to different circuit (from different breaker) in house. A monster 3500 helped when I had similar problems w/ amp. Get the balance control checked. Only thing if it is not the balance, you have left and right out of phase with each other. Good luck. I really would go to good dealer/shop with this ??