I had an ep500 that rattled one time and wasn't sure what the problem was. Axiom sent me a new driver, then a new amp, and finally a replacement sub. Either the port or cabinet must have been rattling, or I was just over driving the damn thing and was hearing crazy port noise. I think it must have had an issue as I haven't had any complaints with my replacement. That being said, I did put my original one through more of a torture test as part of testing it out.

-David