I purchased an Epic Grand Master 350 System about 9 months ago. I've noticed a 'popping' sound emanating from the EP350 Sub-woofer sometimes. The sound is inconsistent, meaning that it may not happen for a couple of weeks then all of a sudden I'll hear the popping maybe once a minute for several minutes. I'd be interested to hear if anyone else has had this problem? Anyone know what the cause could be?