After some noise identification please, 2008 E70 3.0sd.
easiest described as a dull actuator pulsing sound when demand for wam air is set, it does not differ on fan speed or engine speed, it does not alter when selecting between driver and passenger air flow settings, only time it goes away is when you turn the fan (system) off entirely or reduce both driver and passenger temp to coldest setting.
This is a video I found of somebody else’s car with the exact same noise.
I have the IHKA ‘High’ system and have changed the water valve as following the system it appeared the most logical as it controls the heat and is electromagnetically controlled pulsing porting hot water to the heat exchanges, but anyway still have the same noise!!
Considered the servomotors for all the various flaps but as there are 2 ie left and right for all settings I dismissed these. Only single ones are for demist and this does not fit the fault.
Any help much appreciated.