how to fix a vibration/rattle in the rear view mirror

Are you speaking of the rearview mirror on the windshield? If so, it sounds like the mirror is loose on the anchor. It may need to be re-set and tightened. Careful attention should be paid to make sure the anchor is not loose. If you are speaking about an outside mirror, you will need to have that looked at as well. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops