I recently bought 2 EP500s. One had a bad rattle from the get go. The other developed a bad rattle after only two days. I removed the driver from one sub and noticed that the voice coil had come unglued from the cone (woofer part). On the other sub this did not seem to be the case but did notice that the voice coil did not operate smoothly when manually moving it in and out which could have been causing the rattle noise. After calling the exceptional Axiom customer service line, they sent out 2 new drivers. All is well so far. Your problem sounds exactly like mine. I'd call Axiom and have them send out a new driver. There must have been a bad batch from China recently.
