I had the same thing occur, (or at least sounds the same). I had hauled some tomato plants last spring. When I unloaded them I noticed one of the sticks was broken. When I put the top up I got the beeping you mentioned. I found a small piece of a sick from the tomato plant in the top that was causing a bind. When I removed it the beeping stopped. I think there is something causing your top to be in a bind.