Noticed there was a loud rattle depending on my music and how loud it was. Took off the door panel and noticed the foam was all worn and falling apart. Is this the only source of the problem or could I possibly have to replace the speaker itself?

 

The foam surround serves 2 primary functions: 1) It isolates the sound pressure between the front and rear of the voice cone, and 2) its keeps the voice cone centered and aligned with the voice coil.

Re-foaming the speaker is a fairly easy DIY project. Check out Simply Speakers' re-foaming kit on Amazon.com