Car is '97 E320. When I pull away from a stop with the car in "drive", there is a brief period of clicking/chattering in what appears to be the shifter.

The problem is more pronounced if I am headed up a grade and the car is under more of a load. I find that if I pull back the shifter slightly to its stop, the noise does not occur. The shifter handle does not appear to be loose in any direction and works as designed. Any ideas? Thanks.