I agree with fender62 Dave. I had a speaker unit pack up on me some years ago. It was one of three units in the cabinet and one of them started buzzing when driven. The voice coil had come loose inside and was not repairable. The manufacturer (Bowers & Wilkins) sent me a replacement unit which was easily bolted in and reconnected. The setup has been fine ever since. Some speakers have a 'cross-over' unit in them, to send the various frequencies to the relevant speaker units, but I suspect yours, being part of a surround system, will only have one driver unit in it.