I just solved a problem with an irritating rattle in the driver's door of my '99 SVT. After taking off the door panel three times, I finally discovered that the problem was that the inner metal portion of the door was cracked at one of the three bolts that holds the power window motor. The crack was not visible until I actually removed the bolts that hold the motor assembly. Previous to this I had just confirmed the bolts where tight.
I repaired crack by epoxying a fender washer over the crack in the bolt hole. At the same time, I used fender washers on the other two uncracked mounts. I also epoxied over the cracks which had started to spread from the bolt hole.
Door no longer rattles, creaks, or groans. Driver's door will probably crack first, but I guess it could happen to any door.
Good luck,
Marvin Stockman