I hear a random low booming noise .

Are you playing the 1812 Overture when this happens?

Could you please be more descriptive? Does it boom when playing music or just sitting there? If with music, how loud. What do you mean by random?

Could you describe the boom? I've never heard that term used to describe an audio problem.

Herman, this is a very short and dull "boom" that happens randomly meaning no discernable pattern. I can best describe the sound as like that of a subwoofer, but very short in duration (kind of a pop but at very low frequency). It can be heard between tracks or during, but only in silent or low passages. As far as frequency of occurance goes, it is more of a periodic nuisance than a continuous problem.

If it only happens while playing music at low volumes my first suspect would be the source. Do you have more than one source to try? Maybe a portable CD player you could hook up to see if it does it too?

If there is DC leakage, that can be a problem. I had same issue once with a pre. It was a bad resistor; shipping cost more than the repair. Try to isolate it to one component, then you will probably have to bring that unit to repair.

Does it happen in just one channel of both at the same time. Herman raises an interesting point about the source.
Have you found any additional information to share?