I bought a sub from someone and it was shipped UPS. Upon getting it set up I began to hear something like plates rattling. I was initially excited as I thought this was the deep bass I had been looking for, but after removing all the offending parties the rattling persisted. As I was doing the THX subwoofer test I focused on the sub visually and knew that the rattling was coming from inside the enclosure. Knowing that UPS aren't the carefullest of sorts, I opened the sub hoping to find something rattling inside, but no luck, the rattling was internal to the woofer itself. Pressing on one of the passive radiators to make the woofer itself move, the rattle persists even with no power. The rattling appears to be located somewhere near the voice coil or at the top of the magnet. Is there something I can do? The Woofer is an AV12 if that helps at all. There are no screws anywhere on the woofer than I can find to "tighten" anything.