Can you give more specifics, as I have not heard this before. Are you using with spacer or without spacer? Do you have aftermarket engine mounts (I know mine made EVERYTHING shake). Is the engine RPM making the mirror shake, or is it the road vibration?
I have the hardtop spacer and I do have sport inserts for the engine mount. i am only concerned with the vibration when driving the car. I can grab the mirror and stop the vibration. it is the tension between the ball and the mirror.
I was think of putting some type of tape between ball that it rotates on and the mirror.