is it a loose door panel or speaker, etc.?

 

take the door panel off and the three nuts that hold the mirror on inside the door have washers connected to the nut (one piece) and they rattle because the nuts do not tighten down enough to keep the washer from rattling. remove each nut and add an extra washer then tighten them down, had to do both my doors and my truck was a week old! solved the problem!