ASD is the locking rear differential, right? If this is the case, then the problem may be the differential isn't quite unlocking. This will be unoticeable when the car is going relatively straight, but upon making a sharp turn, the outer wheel must travel further than the inner wheel. If the diff is locked, or partially locked, it means that both wheels must turn at the same speed. Obviously, this will complicate turning, and so if the diff is only a little locked it may make the grinding noise, and it may go away at speed because either the force of the speed causes the diff to unlock or the electronics behind ASD cause it to shut down at speeds greater than 50mph. Just a thought...

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2002 Mercedes-Benz E320 4Matic
1995 Mercedes-Benz E320 Wagon
2005 Land Rover LR3 V8 SE
1999 Audi A8 4.2L quattro