According to the Technical Manager @ my dealer, there have been a few complaints from owners of early production cars of excessive wind noises. The causes have been either misaligned windshield (it only takes a 1mm shift to produce excessive noise), driver's side mirror or B pillar trim.
My 335i (mid-October build) is very quiet on the highway.
As for your comment about build quality, I have been told that warranty claims for F30 are substantially less than they were for E90. My own observations, comparing previous E90s that I owned to my F30-335i, suggest that the build quality has been improved. For example, the paint finish is flawless on my F30, the interior trim is of a higher quality and the doors shut with a more solid feeling thunk than the E90 doors.
When comparing the body shells of E90 and F30, the F30 feels more robust on the road and it rides better. The body structure of the F30 has been substantially strengthened over that of the E90 - that's why the F30 feels more robust !!!
Over the past 25+ years, between my wife and I, we have owned several MBs and more than a dozen BMWs. The MBs have always been more problematic with many repeat visits required to fix annoying issues (eg. faulty auto transmission, rattles and squeaks). I would never go back to MB because of the lousy and very expensive service offered by their factory owned dealerships.