In my Honda days this noise was a common beef...
Here is a link to the product recommended as a fix.
http://www.amazon.com/Honda-Genuine-...=5336118868-20
I'm sure it would work on a Bimmer.
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2013, AW, xDrive35i, M Sport
Package, Technology
Package, Dynamic Comfort
Package, Premium
Package, 3M Clear Bra, Euro foglight switch, a few coded fixes