Look inside the queen cup and see if there is a larva in it or if it is dry. The bees seem to like to build dry queen cups. I call them just in case cups. If it is dry it is normal if it is not dry there is somthing about there queen they do not like. If they want to replace her you can not stop them. If you knock it down they will build it back. Let them raise a new queen or get a new queen and pinch the old one.