I have the same issue and I called everybody and anybody.
First off my car is from the states so it should be covered under the 8 year/82000 mile extended warranty.
No canadian BMW dealership will fix your rattle, the extended warranty does not even show up the their system.
So I figure Ill call BMW Bufallo, let me tell you, it doesnt look too promising either
If somebody is successful in doing this, please let me know