Welcome. Don't take offense, it's all in good fun.
My M3 makes a lot of wierd noises, both starting up and shutting down. It's not a Lexus, and for that I am truly grateful.
As to your particular car, diagnosing "wierd noises" is next to impossible over the internet, which ought to be apparent if you stop and think about it.
Is your car under warranty? If so, then stop by your friendly BMW SA and grab a cup of coffee while he or she listens to your car shut down.
No coverage? Try to find a good indy, perhaps using bimrs.org to locate a shop near you that specializes in BMWs.
Character does count. For too long we have gotten by in a society that says the only thing right is to get by and the only thing wrong is to get caught. Character is doing what's right when nobody is looking... " --J. C. Watts