I was just driving back from vacation early morning and had my arm on the window and noticed something flapping in the wind. Looked to my passenger side and nothing so then I started looking in the mirror and noticed I had a door pillar cover flapping, particularly when I'd get above 65mph.
Brought it to the dealer and when I was there we realized 4 out of the 6 had this problem. Service advisor indicated this was a known issue and its a replacement part with a new design. Was under warranty so I lucked out and got free replacements.
The covers are secured by a bolt at the bottom and its the middle or top that flaps. I thought I'd share as I had 4 out that I didn't realize and they must have been doing this for some time. You can easily test by just pushing on it in the middle and top and if there is any give, it probably needs to be replaced. I've seen on other forums some people use silicon to fill it if its out of warranty and it seems to hold.