Mine did it a couple of times then quit. Seemed out of balance for some reason...like it had mud on it...but we have no mud so when I liked at it. it was clean. I think ..because it did it cold..that cheap Chinese motor has some dry bearings already cause when it's warm it doesn't do it...and hasn't done it sense the temps here went over 90. Just something else that will need to be switched-out sometime I guess. Fortunately ebay had some good ones for cheap.