Same here on an 08 M5. Cracking sound from base of windshield area when cold. People keep talking about that TSB but I don't see one for the 5, only for the 3. Has anyone had a dealer successfully perform the TSB on the 5 or actually solve the problem?
I can let you know (hopefully) this evening. My dealer has ordered replacement windsheild trim (interior) that he thinks is the source. Should be getting my car back after work today. Having the windshield re-sealed by a glass guy didn't help. Thankfully, I'm not out any $$ so far...
So how'd it go?
Sorry - it got CRAZY yesterday. Well, the dealer still has my car. After replacing the trim (see posts above), he said they can still hear the noise, so he's got a call in to his technical rep to see if they can troubleshoot it.
Oh, well, they're giving me a rental to drive at no charge to me, so as long as it doesn't take a month or something, I'm fine (so far).
I had it in my '07. Took it in a month after I bought it, and they fixed it.