I purchased an Atlantic Technology 272 powered sub to go with the rest of my AT 270 set. I bought it used and it was supposed to be in excellent condition. Anyway, it just arrived today and I set it up and calibrated it. The problem I am noticing is that I seem to be getting quite a bit of distortion with the volume up. At times the cone starts making quite a bit of a rattling noise. Anyone have any suggestions that could fix this or does this sub sound like it is damaged?