Wind whistle from base of sideview mirrors

There was a similar thread to this I saw when I had the whistling. Its caused by any one of the 3 bolt hole tape covers being ripped, then acting just like a reed in and reed instrument (think saxaphone) I just pulled off the ripped one and left the other 2 on. I was wondering if they were there to help aero or what? Any more feedback on the 'tape for shipping' theory? Tried packing tape, but it wouldn't stick, maybe I need to wash my car again...

 

I replaced my mirror covers with the signal covers so I too had those 3 screws out. I replaced the thin plastic cover with some clear bra/headlight protector and the whistle is gone for good. Can not see the clear material on the bottom of the mirror either.