I have noticed that M1 0W40 starts getting noisier in my N52 at 7,000 mls, which is about when I change it anyway (1/2 the factory change interval.)
I've been happy with M1 on this car, and my previous E46, but at the next change I'm changing to GC 0W30. I've been under the impression that M1 0W40 was a Group IV PAO oil, based on what I had read, but now I believe it is hybrid of Group 3 & 4, while GC is a true Group IV. Probably no big deal based on my change interval, still I want the best oil I can get that's approved by BMW. And I live in one of the hottest populated places on earth.