Sounds as if you overpowered your speakers a little. What seems to have happened is that the coils melted and became deformed (through mechanical failure, the coil would be scraping the magnet). Otherwise, this should not happen under any normal circumstance (or listening at moderate volumes, anyways). This happend to me before when I actually took a driver apart from a cheap speaker by seperating the magnet from the cone (for experimentation purposes). The coil actually melted the "paper" cylinder and caused it to scrape against the magnet. I wouldn't bother trying to fix it doing this, taking it apart you've pretty much ruined it. Buy better speakers that can handle more power.

Or, when I was younger and couldn't afford a darn thing, I acually took a cloth and placed it behind the actual driver (between the spider and the cone) pushing it out a little to prevent scraping. My music seemed to have played fine and I noticed little difference...