MurrayG

I have a buzzing that emanates from behind my dash. It is loudest if I put my ear near the start switch. The sound is much like a small fan making contact with something. To all you experts - what parts live behind the dash that could make the noise described below?

Here are the symptoms:

• It starts when I start the car, and is loudest for a while right after starting the car.
• It usually subsides - but slowly. So it often lasts 5-15 minutes but sometimes only a minute after starting, sometime an hour. It will get louder and quieter.
• It is not uniform - it varies a bit and sometimes stops all together
• It is independent of (does not vary with) RPM
• It is not affected by shutting off the heating / AC system or changing the fan speed
• It does not stop when I turn the car off, nor even when I open the door after shutting off the engine (so it is still going after shut off the car and open the door, but stops a minute or two later)
• It sounds mechanical - it is not a secondary product of vibration
• The car is not throwing any codes

Here are a few recordings I took of the sound. As you can see it varies and is not "smooth".

This site does not seem to let me upload videos nor link to them, so if you paste the below into your browser and replace the <dot> with an actual dot (no spaces), you should be able to see the three videos.

https://photos.app.goo<dot>gl/LiHWNfs6GkXC3Dzx8

So - what devices live behind the dash in that area that have moving parts and could make that kind of noise? It would be great to have an idea before I go opening things up.

Thank you so much!

MeltdownSpectre

The COMAND head unit has a small cooling fan on the left side as shown in the picture below. The fan is right behind where the start/stop button is.

MurrayG

Oh boy -that does sound like a likely candidate. Maybe if I am lucky, there is simply something in there that can be blown out. If more than that, I wonder if the fan can be separately replaced.

In the meantime, I will look for the command unit removal instructions for that vehicle (if anyone happens to have a link, a pointer would be wonderful). It is a 2015 e400 cab - A207.

Also - a bit thank you Meltdown for the very useful response. Much appreciated.

MurrayG

I found a video which describes the removal of the command unit in case anyone is interested:

MeltdownSpectre

That video is where I got the picture from. I remember seeing the cooling fan on the head unit in these videos when I was considering doing one of the CarPlay/Android Auto retrofit to my W212.

That particular video is quite detailed and has really good instructions on how to disassemble the dash. Do update this thread with your findings since I'm curious to see what specifically is causing the fan to make that noise.

MurrayG

Absolutely. Mine is an A207 so somewhat different, bit looking at the car and the video, the principle looks the same.

I'll update here as / after I do the work. I am quite convinced it us the fan - as all the evidence points to that now.

If I am able to separately replace the fan (assuming that's needed), I'll post about that too if no one else has already done so.

All the best.