You need to take the mirror off, pull small plastic trim piece off from inside of door
undo screws that hold mirror onto door undo screw that holds plastic cap under pivot point of mirror
inside it on the base are 3 screws, put some locktite on them and do them up tight, Then remount the mirror, my drivers side one was so loose it made me fear it would fall off while driving, but as I said those 3 screws just needed about half a turn each and mirror feels like new again.....