If your vehicle is showing side mirror housing loose and vibrating while driving, here are the most likely causes and the parts you'll need to fix each one.
The nuts or bolts securing the mirror base to the door have backed out over time or were not fully tightened after recent door or window repairs.
The plastic mounting studs or the base of the mirror housing have cracked due to an impact, such as clipping a mailbox, garage frame, or another vehicle.
The internal spring or detent mechanism that holds the folding section of the mirror firmly in the driving position has worn out or snapped.
The metal on the door itself where the mirror mounts has been bent or fatigued from a severe impact, preventing the mirror assembly from seating tightly.