Starter / flywheel problem

Has anyone had a starter replaced on their XP? Mine had 57K when I bought it, and every once in a while the starter would grind like the truck was already running when I turn the key. They replaced it, and on that one the drive gear would stick to the flywheel. They replaced that one and this one now has ground once, but fine everwhere else. I think there may be a tooth in the flywheel missing or damaged? Any tech's out there want to pipe in? They claim the flywheel is perfect.......OK so how else could this occur?

Follow up

It was ground down on 4 teeth, not sure how. The dealer replaced it and fixed the heat (seperate posts) air in the system.

Seasons greetings!