I just bought a used pair of 15" PV Black Widows. Got them home, tested them, one sounds fine, the other seems to have a rattle in it. This is testing in free air so it's not the cab rattling. Are there any simple things I should check before I contact the seller and ask for my money back? I tested w/ a drum machine crossed over at 125 hz so all I'm hearing is kick drum - the good one goes thump, the bad one goes thrattlump. Almost like if a drummer plays kick alone but leaves the snares engaged on the snare drum so they vibrate in sympathy. These do have different cones - the good one has a blacker cone, the bad one has an older lighter looking cone. I asked the seller if they were recones and he said he didn't know because he bought them that way.