I have the same issue on my drivers side mirror. I popped off the tab underneath and found 4 T10 Torx screws that may be able to be tightened. I only had a T15 Torx bit so I need to find a T10.

On my old 4.6is there were 2 phillips screws underneath the housing that I could tighten up the mirrors with. I guess they changed to Torx on the later years.