2000 Pontiac Sunfire engine problems

A few days after we purchased this vehicle we noticed that the engine made a "grinding, rough" noise when put into park. There is also a vibration that can be felt inside of the car. The first time the dealer looked at the car he said it had a "miss" and he pulled up information in his computer and noted that we were the 16th people to complain of the same problem. He pulled a car off the lot and compared it to ours. It did the same thing. He said there was nothing he could do to correct the problem.

I own a 2000 pontiac sunfire and the car shuts off while driving at 60-65 MPH. Car has been taken to the pontiac dealer, they have not been able to find anything wrong with the vehicle, also left the vehicle with another mechanic who drove the car for a couple of days but it did not shut off. I am concerned because I was driving on the highway in the fast lane and the car just decelerated and stopped.