So its been extremely cold here in NY the last few weeks. I just purchased my car and noticed on the extremely cold days 0-5 degrees, there was a rattle. Sounded like it was close to the front on the driver side. I havent gotten underneath to take a look but it wasnt doing it when I first got the car....Almost like an exhaust shield or something, metallic sound. This is my first BMW and I've been doing research day and night as I always do with my cars. Hopefully someone can give me some insight!
It also does it after the car warms up and when im driving, usually fades with acceleration but it does happen when driving

Thanks

 

It might just be your sunroof. I got the same sound and it bugged me for years. I finally found the culprit and added some extra padding. Fixed it quick. do you notice it is happening when you hit slight bumps?

 

Rev it up a little and if you hear the rattle while the rpm decreases it could be the waste gate. Just had my turbos replaced by the dealer 3 months ago because of waste gate rattle. It's common on 08 535i's. the good thing is, it's such a common problem, they replace em for free.

 

It's more under the car and can really only be heard when outside the car

 

I'll have to give it a try, it sounds close to like heat shielding hitting the exhaust or something. It's finally warming up so maybe I can do some more diagnosis.