I took the carpet etc up in the trunk and found a vent of some kind in the trunk on the left hand side below a removable cover, it is around 6 in long and 2 in hi. has a cover hanging from it that would blow open. Any one have any idea what this is for.

 

Its to allow air pressure to be released when you close the doors. If you dont it will feel like a pop sensation in your ear. Mercedes makes the windows go down and up auto to prevent this as well. My guess at least. LOL.

 

I think Audi does the same thing, it's a slick feature. But I have no idea about the OP, but your theory makes sense.