Rattle from passengers door.

I have searched high and low for a thread about this subject but can't seem to find anything. I am having a annoying rattling noise coming from my passenger door card when listening to loud music. It doesnt have to be stupidly loud. Even just background noise and if it hits the right bass note's then it will vibrate. Just curious as to what it would be and if anyone has had this problem before. I did read that the speaker itself is riveted into the door so i cant imagine that being a problem. Any idea's would be greatly appreciated :-)