I had the same problem about four months after I bought my ‘05 Roadster...noise out of the driver’s side lower speaker. When I finally had time to tackle it, I followed the instructions here for opening up the door panel. I discovered the previous owner had installed expensive French-made Focal speakers. There was nothing at all wrong with the speaker. It turned out to be a bad connection someone had made when installing those nice speakers. What a shame to spend that kind of money on speakers and then have someone install them in a shoddy manner.

If it does turn out that the speaker is blown out or rotted out, there are decent inexpensive speakers that you can find to replace it. If you find that you have an expensive speaker then it might be worth it to use a repair kit to try to fix the cone or the material surrounding the cone. Otherwise, I would be inclined to just replace it.