What causes 1 speaker to distort unexpectedly?

I have Totem Winds and the left speaker, only, will crackle and distort short bass blasts with the bass speaker undulating wildly for a few seconds. The mid and tweeter seem to have a hiss sound on this speaker at the same time. This problem just started today and has gotten worse. Everything is running off space-tech tube equipment, but this has never happened before, and as I said it is only happening in one speaker column.