all tube phono preamp creating a crackling, fire-like sound

Hello
I just purchased an all tube phono preamp from an Audiogon seller. the preamp uses the following tubes:
5u4gb, Ob2, 6v6, and 5 12ax7. My problem is that one channel sounds totally awesome but the other channel is unlistenable with a crackling, fire like sound which a friend of mine said sounds like frying bacon. I have changed all of the tubes except for the 0b2. I have also tried a multitude of various interconnect cables, none of this has made any difference. The sound will go away for a couple of seconds and then it comes back, it also comes in waves, starting off low and then getting louder. I also ruled out it being a speaker problem by switching  speakers and their channel. 
Does anybody out there have any experience with an issue like this, and if so, what was the problem and how did you resolve it? I love this unit and I'm about to send it back the manufacturer, where hopefully the problem will be resolved.
thank you