I'll grab a pic tomorrow and try to explain better.

 

I'm interested where you put the caulk as well. For anyone keeping score, I have round rugged ridge quick release mirrors and my drivers side whistles as well.

 

Sorry. I forgot until I saw somebody else asked :(
In the picture, I'm pointing to the seam where the front bezel of the mirror meets the back. They are not flush. Probably off by 2-3mm. So I just ran a bead of silicon along the lower side of the seam and smoothed it over with my finger. I rotate them and adjust them all the time and it's never made another peep. The RR products get slammed on a lot. But these mirrors are pretty heavy, sturdy and of pretty good quality. The only flaw is that sharp edge of the outer ring that makes it whistle. And very little vibration. I'd buy again.



Stupid thing keeps uploading sideways. But this is basically it. Cheap fix.