We purchased our 2017 GLC 300 in June '17. About 2 weeks ago while on a road trip I noticed an odd noise. The noise sounded like a prop airplane. I took it to the dealership where we purchased it. I took it on a drive with the service advisor who said it was the tires cupping. I'm not a mechanic but the noise was not from cupping tires. They scheduled me for a tire rotation for the following week and sent me on my way. Not satisfied, we took it to another dealership the following day. Again, another ride with a service advisor. This dealership kept the vehicle and 3 days later called us saying they found pieces of metal in the transmission and the transmission needs to be replaced. Has anyone experienced this issue?