Tube Amp Problem

I have a Jolida JD302BRC integrated tube amp. It had been working very well. But recently, when I turned the amp on, during the warm-up period, the right channel speaker would make a couple of loud sonic booms. Then everything is fine, no any problem as long as it's on.

It had not happened before and it does not happen to the left channel. What could be wrong?

Thank you very much for your advice.
Its possible that a power tube arced.

Its also possible that a driver tube could be having some problems.

In either case, it should merely be a matter of finding the tube at fault and replacing it. You can knock on the tops of the power tubes with your knuckles- if you get a response ('sonic boom') replace the tube.