03'55AMG

Late last night, I was working on detailing the engine, and when I was done I started the car and got out to inspect my work again and make sure I got everything out of the engine bay. Well, when I started the car the music was turned up on a cd playing a song with some good low bass hits. I then heard a rattle on the front passenger door. So I shut the car off but left the music on to diagnose it. Turned out to be the trim panel, but I cant stop the rattle. I even took th trim piece off to make sure that's what it was and it was. But I can't figure why it's rattling. Any ideas?