Moin Moin, I’m getting old again – many ask! – When I turn off the ventilation for fast long driving (so not the … here… what’s it called again… not the “indoor air around” but the fresh air supply ventilation…. (please for correct designation!!)))) there is a sec. after the ventilation is on zero a loud bang, or better said a dull blow, than when a thick plastic plate overturns. – If I only had the car with a short ventilation, and then it shuts off, the banging is not so loud or not listening at all. – If the car is turned off with the switched on ventilation, no bang can be heard either. – If I have this “indoor air” bangs it also not at all. – besides, I noticed that the ventilation in first and second stages of the strong braking is starting to beep/quiet, if I don’t have this “indoor air” bangs on it either.