I'm not a fan of stealerships in general, but it could have been play in the wheel bearing that allowed the disc to contact that bolt. You don't always hear the bearing itself going but one damn sure does hear that scraping against the closest surface!

 

I never go to the dealer if at all possible. Their parts are way too expensive. In this case I didn't have much of an option. I was lucky they could do it in one day. Some places can be booked weeks in advance.

I would think that enough play in the bearing to allow contact with the bolt head would be noticeable in the steering but the car drove normally. Before going to the dealer I looked at the back of the disc and could see that rub mark. I think the bolt just backed out due to vibration and started rubbing. I am puzzled as to why the dealership did not do a proper fix on this bolt.