Ok, what I decided to do was replace some of the soundproofing BMW asked me to remove from the plastic wheel arch. They were concerned that the materials may ignite from the heat from the turbo hose.
When I added the sound material back, I was careful to make sure there was sufficient space between the materials and their beloved hose. Straight away that made a discernible reduction in road noise, but not elimination.
I then took another look to see why and found this gap. It's between the left front plastic wheel arch and the rail that runs along the engine bay. The squares indicate where the gaps are.
I only managed to spot it when my car was parked inside the garage and there was really bright daylight shining from the outside & bouncing off the garage floor through the plastic wheel arch!!
To me, that's basically allowing a lot of road noise into the engine bay and hence the cabin. So I proceeded to stuff some rubber foam from the wheel arch side
The gap between the plastic arch and wheel well seems to be to allow some wires from the suspension and some part in the engine bay. I have the adaptive suspension, so perhaps this gap was left there to allow the cabling.
That might also explain why my car is noisier than the other demo F30s which have the standard suspension.
After plugging the gaps, the car is a lot quieter on coarse surfaces, but I was still not quite happy.
Because the car was a lot quieter, I could zero in on the remaining road noise. It seemed to be coming from the left side doors.
As I documented in the wind noise thread, I was going to experiment with some foam around the windows. My gut feeling was that the rubber guides for the windows were not sealing properly.
I did and this is where I applied the sound insulating foam tape. I applied it in a way that would stop any air pressure and sound leaking through the gaps.
Lo and behold, when I drove over the coarse surfaced roads, the car was significantly quieter yet again!
I'll be showing this to my dealer and asking them to replace the guides. I just hope they don't give me the usual "it's within spec" bull$h1t
Anyway, relieved that the car is now fine (or would be if they fixed the windows). It's as it should have been all along... Including sydney's notoriously noisy concrete/coarse chipped roads (proof... They are resurfacing sydney roads with a quieter tarmac rubber compound)
I then think about how bad the quality control is at the Rosslyn plant. The F30 is noisy in my case because of 3 issues:- doors not shutting tightly, bad quality window guide seals, gaps in the plastic wheel arch & suspension tower. I've also had my left tail light replaced because it fell out and the squeaky exhaust flap replaced.
BMW needs to pick up its game in manufacturing quality. Fingers crossed I don't get any serious mechanical or electrical issues.