Mine has done the same thing for 3 years since I owned the truck about the same occurance you have descrbed and hasn't gotten worse, so I wouldn't worry about it. When it does it, just stop right away, let it sit a second and 90% of the time, it will start next time with no grinding. The other 10% takes three tries, but that is only happened to me like 3 or 4 times total.