a creaking or rattling sounds has been coming from my passenger door at speeds above 75mph for years now. it has progressively been reduced to speeds above 60mph. My car now is over 100K and the drivers door is begining to make the same creaking / rattling noise. At first i thought these noises came from the mirror. But now i suspect it is somwhere in the door.

Does anyone know the cause of this? What am I looking for when i take off the door panel?