I have a pair of b&w 602 s2 speakers (3 years old) , connected to a yamaha 595a reciever, the sound from the left channel suddenly became weak and muffled, I checked all the cables, and connections, all seem to be ok, I even connected the right speaker to the L speaker out connection to the reciever and it seems to be ok. Can this be a defect in my speaker, the speakers are hardly used. Please help and suggest. Thanks.