Hissing noise behind dash (a/c on - off)
I hear a hissing sound from behind the dashboard. It gets stronger, then quiets down, sometimes stops, and then starts all over again. It doesn't matter whether the air conditioner is on or off, the hissing noise is still there. The air conditioning refrigerant has been topped up, but the hissing noise is still there. If I turn off the internal air circulation, the noise stops immediately. Very annoying. Where should I look for the problem? Should I try to replace the internal fan?
W211 E220 CDI 2008 sedan






