Mine does this, too. Is your system on Auto when this happens? I always thought it was the AC fan coming on to control humidity in the cabin. I don't ever hear the hissing sound when I manually override the controls and turn Auto off.
__________________
2008 E90 335i // Black Everything // photos
COBB tuned / QTP e-cutouts / Helix FMIC / cp-e DCI / AWE BOVs / Catless / FBO + F15 X5 xDrive35i
|