I have searched the forums and have not really found any info on a cause or fix....I have a 2014 2500 and the drivers side mirror shakes so bad its hard to see anything at times. Its not the glass shaking, its the arm. I can be backing out of a parking spot and you can see it shaking. There is a small amount of play in the arm itself causing the mirror on the end to shake bad. The 3 bolts the hold the arm onto the door are tight...The swivel point is where its loose. There has to be a spring and a set point in there to lock the arm in place when its folded in or out? I have used the water hose to clean the swivel in case there was any mud etc not letting it "lock" properly...Its gotten worse over time and is about to drive me nuts...I hate driving down a back road with the window down because of the rattling noise the arm makes now...