starter problem

[Nlbloch]

My starter will occasionally "stick" in the on position -- that is, it continues to whirr after the floor button is depressed, even after the engine has started. I haven't figured out how to "unstick" it; generally, it stops on its own but sometimes making a large popping noise. I suspect the continued running is not good for the starter.

What could be the problem, and more importantly, the solution?