Fix whistling mirrors
 

I've read good solutions for the rattling windstop, but I haven't seen similar good solutions for the whistling side mirrors.

Has it been identified where specifically the whistling is coming from? It can't be the entire opening between the mirror and the car -- it has to be a smaller piece.

Any fixes?

If you are referring to the 987/997 mirrors then the whistle is coming from the small 1mm gap in the middle. This is a known problem in the 997 cars and I assume it was carried over to the 987. It is because right in the center where the seam is (window side of the large air opening), the seam is lose (about 1mm) and there is no way to tighten it.

http://www.kcrpca.org/files/mirrorwhistle.jpg

The only solution so far that has been a good one, is to use a small piece of clear bar to block the gap.

Whistling outside mirror(s)
 

At least on my 2006 Boxster S the whistling is not coming from the seam shown on the picture (i.e. the seam toward the car from the two webs which support the mirror). I temporarily put a piece of masking tape over that seam and the whistle was unchanged. I then tried tape over the seams around the bottom of the mirror pod itself, and that eliminated the whistle. Based on this I took off the tape, and rubbed some clear RTV sealant into the crack all around the bottom of the mirror (in my case only the right mirror sings- I'm not sure why). I then wiped all of the excess RTV off the surface, so it remained only within the crack. The fix is essentially invisible, but the whistle is gone.
Frank

What is RTV?

Room Temperature Vulcanizing (RTV) silicones are sealants and potting compounds that cure under normal room temperature conditions.