As with most things on this car, when I look at one thing I find at least 3 more issues. This was the case today. I had always known there were lots of clunks and rattles when driving, but chalked it up to the 'character' of an old car.
Rattle source #1: 2nd gen side mirror adjuster just laying in the door.
Rattle source #2: rear regulator bolt hole in door frame had been mangled at some point, so the bolt wasn't actually clamping anything, allowing this leg of the regulator to swing free and bang about.
Rattle #3: petrified piece of tape stuck to...a mirror mount backing plate? Not sure...guessing they taped it inside the door for safe keeping, but it had come loose decades ago most likely.