Hi guys, got the same problem with my GLC400d arrived in August. The problem was first noticed few days ago after rather a long driving on autobahn (220 km). When I just exited and slowed down, I noticed this annoying noise coming directly from the central console, from behind the vent openings, a bit below them. During the trip the noise disappeared and appeared again, usually it was quite during the first 10-15 minutes after start, and then appeared again. I supposed the reason is MBUX unit cooling, because the noise was very similar to a fan on small devices like a video adapter or CD-ROM (if your still remember what it is - and yes, it had a fan to cool it down).
Researching here and on other forums just confirmed it is MBUX. Since few days I have been trying to identify any relation between what MBUX is doing and when noise appears, because it does not come always. It seems I found something, and want to ask you for confirmation - whether you observe the same.
1. I noticed the noise appears primarily when I use Navigation.
2. Just navigation does not always cause the noise, but when it is used with AR (Augmented Reality) enabled on the map (that fancy blue arrow appearing on the top of the picture from the front camera) the noise comes almost immediately.
3. Sometimes the noise appears when I use audio commands for few consecutive orders.
Anyone having the same issue, could you please try to drive with MBUX enabled and doing navigation for 20-30 minutes with AR enabled and without it? Better you drive in a city, so AR is shown more often. Does disabling the AR make any difference to the noise?