I hear a random low booming noise .

I think that what you are hearing is the woofer bottoming out from some DC leakage. Not a good thing.

Thanks Swampwalker, do you think this could be from a malfunctioning tube in the amp and/or preamp or would this be a symptom of bigger problem with amp and/or preamp?

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.