I’m hearing a grinding noise from the front end of the Jeep upon acceleration in 4wd drive. When I make turns the noise is louder and there is a binding feeling as if the brakes are being applied. None if this happens in 2wd. My mechanic has replaced worn u-joints, track bar, carrier bearings and has inspected the front axle, differential and transfer case and things look to be fine. Any suggestions would be appreciated.