Similar problem here. I had a rattle and I thought that the wires touching the amp boot or perhaps the port was causing the problem.

See this thread:

http://www.axiomaudio.com/boards/ubbthreads.php?ubb=showflat&Number=192062&fpart=1

a picture of my attempted fix can be seen on the seconed page of the thread.

Unfortunately I still had a rattle and axiom ended up sending me a whole new sub after trying a new driver and an amp.

-David