It sounds like either the voice coil is on its way out, or that one of the tinsel leads from the terminal to the voice coil has worked itself loose.

Either way, we'll get it taken care of. But, to answer your question, you can just unscrew the woofer from the front of the enclosure and visually inspect the woofer and wiring connections to make sure that no wires are loose or torn.
If you don't see anything, just give us a call so that we can get this handled for you as quickly as possible.