SIB SI B51 13 04
E60, E61 (5 Series sedan and sports wagon) produced up to June 2007
E63, E64 (6 Series coupe and convertible) produced up to June 2007
A rattling noise may be heard from behind the center display or lower windshield area when the vehicle
is driven over bumps.
The retaining bolts for the cross strut brace on the center support bracket, or on the strut towers, have
worked themselves loose. In some cases, the threaded holes of the aluminum center support bracket
have become damaged.

This is a very easy DIY fix. You can get full access by removing the cover at the rear of the engine. I just tightened them all down and it's been quiet ever since.