I have the exact same issue on my white on white MY LR AWD with Geminis. Early August build date, 35xxx VIN, less than 1,000 miles.
Made a service appointment the other day. They kept the car for a few hours, messed with the window and the mirror, and ultimately determined it was the exterior mirror applique making the noise. They didn't have the part on hand, so they gave me my car back and told me they'd order the part and install it at my house next week. All under warranty.
Here's the part info they emailed me:
Parts Ordered
A-PLR APPLIQUE, EXT.MIRROR LH MY
Part #: 1495632-00-A
Hope this helps you.