Here's a step-by-step door panel removal explanation courtesy of member engatwork:

http://12.96.14.5/~engatwork/CkStrap.htm

As far as that rattle goes, I'd wager that it's a loose screw that holds on the wood trim from the inside. They loosen over time so be sure to check 'em.

Good luck!

~Paul

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'91 300E, 208k miles