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.
Well, I guess my 07 Z4 Coupe (auto trans) isn't normal, because it doesn't make any hissing noises at all... at least, none that I can hear. My suggestion... Try another dealer.
I believe that this is what I should do. Getting the tech at my dealership to look at this problem has been like pulling teeth.
one possibility... We had a hissing that was related to the brake booster diaphragm (Vacuum) leaking, though it was rather constant. Yours sounds like it is torque related, ie engine twisting in the mounts during acceleration... you probably have a defective vacuum hose or element in the vacuum system that leaks a little when moved just a bit. You can push and pull the various vacuum hoses at idle to see if you can cause the sound to happen. Chuck
