OK, after 20,000 miles, I have my first problem

The a/c vent in the center of my dash on the left side rattles very loudly after the car has sat in the sun all day and the a/c is blowing full blast and the vent is pointed at the driver. If I re-aim the vent towards the passenger it stops rattling, and once the temps come down it won't rattle no matter where it is aimed.

Has anyone experienced this?

I am thinking about having the dealer fix it, but I am worried they might cause more rattles by taking the dash apart.