Mercedes ML 350 2006

After I’m driving for awhile, and put car in reverse, and start to maneuver out of a parking space let’s say ... I hear a metal on metal sound. It only happens in reverse...and only if I’m turning the steering wheel slightly. Does not happen in drive. And if I’m reversing straight back without turning the wheel, it does not happen. Side note...I may just sell the car to Car Max..it has cost me sooo much money this past year. Only 74,000 miles on it. But looks brand new!