hissing noise

Hello, I hear a special hissing sound when the ventilation is on. It is heard constantly, when I turn off the ventilation (I set the fans to 0, the sound stops). Does anyone have experience with this sound and what could it be? It is an A-class A180, W177, 2018. year...

I have a 2013 C63 coupe. On a drive out a couple of weeks back it started to make a hissing noise that can only be heard inside the car, and that seems to be coming from behind the central part of the dash. I've since determined its related to the climate control/heater functions. The noise...