Here are a couple links to other threads on this subject:
http://www.babybmw.net/forum/viewtopic.php?t=89767
http://www.babybmw.net/forum/viewtopic.php?f=74&t=73418
recordings of the noise:
https://vimeo.com/183449790
https://dl.dropboxusercontent.com/u/...ox%20noise.m4a
https://www.youtube.com/watch?v=KnbkF5LpUlE#t=31
Updates on my car -
I found out that they also tried replacing the turbo. Not sure if they left the new one in or not.
Also found out that the box they ordered is a remanufactured unit. Apparently that is the only option available from BMW. Hopefully it's remanufactured to be as good as new by ZF. It is covered by remainder of 4-year warranty at least.
Colin