You might want to check with Weasel56, he had a good comment about a similar issue on an X5 that was shaking intermittantly. He said to unplug the wire going to the electric motor on the driver's side of the transfer case; which would essentially put the vehicle in 2WD mode (rear wheel drive).

Of course your problem is different since it's a grinding/scratching noise rather than intermittant shaking, but it's certainly worth a shot.

Here is the link to the other discussion if you want to read it:

http://www.xoutpost.com/x5-e53-forum/...wobbly-x5.html