Originally Posted by thekurgan
Holy shit! That is one expensive noise fix! You never noticed any flow issues from the HVAC I take it? This is a good find and I imagine all Z4 owners may eventually have this issue, coupe and roadster.
Actually I did have air flow problems very sporadically as well. Difficult to replicate so it was a pain to get the dealer to fix under warranty as I could not reproduce the problem. It would happen maybe once a week on its own and I could get the problem to go away simply by cycling through the vent settings. One day when it happened (no air flow out of any vents, but you could hear the air blowing - where it was going no-one knows) I drove to the dealer and showed them the problem.
Dealer claims the air flow issue was/is unrelated to the noise problem because the noise problem had not yet started when I took the car in for the air flow problem.
For the air flow issue they replaced the HVAC control panel. To access the panel you have to remove the center dash vent and radio so labor is not that expensive, but the control panel itself is expensive. I think the panel (the automatic one at least - three knobs that control air temp and fan speed) costs close to $900 for the part alone (a few hundred less for the manual version). However, replacing the panel did not solve the air flow problem, it still happened sporadically. I told them its an actuator, but they said no.
I'm thinking/hoping that the airflow problem was related to the broken gears and broken plastic shaft that they fixed, but I haven't had my car back long enough to say for sure.
For what it's worth the broken plastic gears/actuators/plastic shaft from the air box/flaps is not a problem isolated to BMW. Friends I spoke to said they encountered similar problems with their Lexus, Ford and Volvo cars. And my old Jeep has a similar issue as well.