I keep hearing a grinding noise coming from the rear, any ideas what it could be

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I usually only hear the grinding noise when turning. I've heard with Ford Taurus it's a common problem. Mechanic said there's nothing wrong with it and it only makes that sound because it's awd. B.S. I've only driven awd cars and never had this problem. I thought it could be wheel barring, rod,or axle. Anybody have similar issues? I will be taking the car into a different Ford mechanic.