I created an account, just to add to this 7 year old post. Because, as you might guess, I had this problem too suddenly with my SM3. One day it was fine, the next the vibrator was getting stuck up. Checking everything I discovered that the rubber matting I put it on the stop it from moving around and make it quieter, had a wrinkle in it and was pressing up on the machine from below. Flattening this was all it took to restore good working order. So, moral of the story, might be an uneven surface the machine is on - worth checking!