Many years ago i used fly a Queenair on regular charters. Once i was on decend through 6000 in to Darwin when suddenly i felt this severe vibration coming through the control column that even prompted a comment from the punter sitting next to me" I did not know this aircraft was fitted with a stick shaker!" It continued until we landed.
Upon investigation the LAME found that it was caused by a worn bush in the elevator trim tab.
I think it has prompted an AD being issued for all Beechcraft at the time.