The noise floor sounds like hissing. You really need to get to the root of why the channels are off. Try all new batteries, swap cables and mics, and see if anything changes. Otherwise, might need to get it checked out. With the show you have, you can try normalizing each channel separately, and see what happens. I have done this once or twice, in odd, off center taping setups, where one side came out significantly hotter than the other.