I had a similar issue on my 2007 X3. I would hear a clatter at cold starts from the muffler. It was the flap/vacuum on the exhaust. Fixed under warranty.
My garage: 2013 BMW 550xi GT, 2007 BMW Z4 3.0si Manual, 2006 BMW 530xi
Retired: 2007 BMW X3, 1998 BMW Z3
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