Posted by Steve on December 29, 1998 at 08:15:29:
In Reply to: May be regular recalibration of duct valves (more) posted by artie on December 28, 1998 at 16:54:55:
My 98 E36 makes these sounds as-well. It is explained in the reply below and your manual.
: I don't know it this is the cause, but like the previous E36's, the E46 has a sort of calibration cycle for the valves in the heating and cooling ducts. They will open and close in order to recalibrate themselves. This happens every once in a while and is described in the owner's manual.
: Alternatively, I have heard a high pitch, low volume whine at times - but ususally in times of very high humidity. I believe this is also related to the environmental system and my be used to decrease the humidity levels. In any case, if everything works, don't worry about it.