Bucket

I've had these speakers for almost a year. They sound great, but lately, my sub has been acting funny. Sometimes, it will just sort of rumble occassionaly even when there is no sound playing. And when there IS sound playing, the subwoofer is VERY boomy and loud. The sub level control has little effect, even if turned all the way off. How can this be fixed? For what I paid for these speakers, I expected them to last longer than this...