7.3L diesel starter problem?

I have a 99 ford f-250 powerstroke. the starter works fine and starts the vehicle, but the starter drive (the gear which contacts the flywheel to spin it) does not stay in place after it is started and will hit the flywheel from time to time making a tinking noise after it is started. i am wondering if someone knows if this needs a new starter or if it just the starter solenoid. thanks