Join Date: Oct 2008
Location: Ontario, Canada
Car: 2017 OutBack Premier
Feedback Score: 0 reviews
What Midas is referring to, is that the mirror glass is clipped to a plastic plate (about 2.5 x 3 inches)that has the motor pivots for moving the mirror. If the clips haven't entirely locked into place, the glass may be able to vibrate. He's suggesting pushing the mirror entirely back into the mirror enclosure to see if you can lock the clips.
On my 2005 Sierra dually I've had the same issue and finally added a small glob (1/2 the size of a pea)of silicone seal at the edge of the motor plate and the mirror glass on two edges of that plate at the mirror. After it cured overnight, the vibrations were gone. And a razor knife cut through those silicone globes would allow unclipping of the mirror glass if needed in the future for mirror glass replacement.
BUT ... your car is under warranty! Take it back to the dealership for repair.