The BAT mutes the output for 50 seconds at startup to avoid the problem Elizabeth mentions. The crackling is not normal. I get a slight hiss coming from the tubes but I can only hear it if I put my ear next to the tweeter. It's not volume-dependent, I can't hear it from my listening position and I certainly can't hear it over music.
You mention that the replacement tubes are nearly new. Do you know where the previous owner purchased them?
It sounds like it may only be one tube. You could identify it by swapping one pair of tubes at a time from left to right. When the noise moves, you've found your bad tube. The problem will be to find a matched tube as a replacement. I'd opt for replacing all of the tubes at once. That way you know exactly what you've got and how long they've been used. Everybody has a different idea of "expensive" but I just retubed for less than $250 and my last set from Kevin lasted well over 5 years. - Dick
