Welcome. The only 2 things I have some info on:

2- Could be your tensioner pulley - Does it rattle more time if you let the car sit for more than 1 or 2 days?
5 - My previous 4.4 did not really have any knocking sounds but it is a little louder at idle than the 6 cylinder.

Did you have the car scanned with any BMW software yet? That will show any potential stored codes in the engine.

Save this link for future reference also.
Xoutpost.com - Xoutpost.com x5tips.htm