I have noticed a distinct hissing sound (like the sound a very thin water jet) whenever I step on the throttle. This usually happens between 1750rpm and 2500rpm. Even a slight acceleration causes this. I do not hear the sound when I am not throttling. I reported this problem as soon as I experienced it, in August last year, but the tech was unable to diagnose the cause of the noise. After repeated followups the technician finally said that this is 'expected behavior' and that they have been able to produce this noise on other 07 3.01 automatic transmission Z4's, but I can't believe that this is OK or acceptable. In all honesty I don't think the tech actually verified this at all.