Thought I'd ask the audio forum about this, you guys probably have a lot of experience w/rattling rearview mirrors

Mine isn't necessarily from my sub...it only acts up when the car has been under direct sunlight/heat for a while. And when it rattles, it rattles on the smallest bumps, and goes crazy when bass hits, even low-volume.

But when it's been in the garage or has been sitting outside during the evening, no such issue - the rearview is tight and stays put even at high volumes. No rattle.

What's up? Why is it temperature dependent, and do you guys have any suggestions on remedies? Thanks