Well, it could be the front drive shaft, the chain in the transfer case or the rear drive shaft.
I still have the metallic clicking sound in the conditions described above. I replaced the front drive shaft with a longer shaft, the chain and even the transfer case and click is still there. The splines are perfect. One indy mentioned that the clicking sound comes from the rear driveshaft.

__________________

4.8is 2004 imola red
4.8is 2005 Black on Black - DINAN/2 sold
4.4 2004 X5
2003 330xi
2008 328xi - sold
4.4 2000 X5 - sold