Which HVAC control panel do you have...the IHKA or IHKR? THe IHKA (auto/digital control panel) has a small fan that sucks in cabin air across a thermister...which is how the IHKA maintains the temperature that has been set.
This fan is also on the P-bus which continues to run certain items on the P-bus up to 16 minutes after shutting down the car (just like the little orange light on the gear shift plate). If there are no calls on the door handles or remote buttons on the key...the car will go to SLEEP and the little fan & orange light will turn off. Any time you lift a door handle or press buttons on the remote key...the car will AWAKE and items on the P-bus turn on.
Again, that little fan can get noisy from a build-up of dust that accumulates on it...take note of the vent on your IHKA panel...if it is full of dust...so is that little wheel:
(is this the IHKA control panel you have?)
(or do you have this IHKA control panel? if so, the fan is up & behind the left vent)
(small fan inside the IHKA control panel that makes that little buzzing noise for up to 16 minutes after shut down)
... How would I access this fan to clean it and might I start breaking things if I try!?! I am happy to try stuff, but am not the most skilled, also not the worst.
Any advice and help would really be appreciated please.