TLDR: Rearview mirror hangers can trick the autodimming mirror sensirs.

For weeks, my auto dimming mirrors (side and rearview) have been stuck 'on'. With the short days and non-instant on/off, it was very hard to pinpoint why the mirrors were dimming when they shouldn't be. Finally, my wife and I covered the sensors on the rearview mirror and it went away....until we exposed them again. Frustrated, I grabbed the mirror again...and I felt another sensor on the back of the mirror. It turns out there is a sensor on the back of the mirror looking out the front windshield-and it had been blocked by a parking pass which I had 'tucked' up out of the way. Pass was moved, sensors could see properly, and now the autodimming is back to working perfectly. Phew!