One problem related to engine grinding noise has been reported for the 2011 BMW 335. The most recently reported issues are listed below.
Driving 40mph, smoothly at consistent speed, in middle lane of 3 lane road during morning rush hour. I had been driving for about 10-15 minutes after car had been in garage the night before. Attempted small acceleration, car did not respond, engine had turned off unclear if before or at time of attempted acceleration. Power steering was off. I put on my hazards, slowly drifted to stop, put car in park, attempted restart, first attempt failed, waited 15 seconds and second attempt successful. For next 3 hours, the engine had a rhythmic grinding sound which then stopped. Fuel tank had been filled the day before and was not near empty. Took to dealer, they have not been able to replicate event or find anything to fix.