'92 323 Astina BG side mirror shaking
 

Hi, new user and first time poster here, and I figured this would be the most appropriate place to ask this question.

I've recently purchased a 1992 323 Astina BG, and whilst the car runs perfectly I've come to notice the glass in passengers side mirror shakes violently when I do anything over roughly 50 KM/H. Likr I said, overall it just appears to be the glass, as the mirror itself is solid.
So my question is; short of trying to find a replacement mirror is there any sort of fix I can manually make to the mirror? Definitely not going to start opening stuff up without knowing what I'm doing.