I was working on my other car and the Benz was parked next to it, and again, I hear this squeel/buzz sound every 30 seconds or so. Its not a regular interval between every one. So I pop the hood and from the best that I can tell, its coming from whatever accessory is all the way on the bottom of the driver side (A/C Compressor? P/S pump? there are pressed lines going into it)

It really sounds like some sort of electric servo actuating. This is with the car off and the key can be in or out, any position on the ignition, as long as the engine isn't running (well, maybe it happens when the engine is running, but I can't hear it)

2007 C230SS M272

 

SSM - Bottom pulley is Aircon compressor. Are you sure the sound is electrical & not the refrigerant settling down. How long after shutting down the car can you still hear it?

 

I guess it could be the refrigerant passing through a small passage. It lasts about a second per occurance before the longer ~30-60 second pause. I have only really noticed it shortly after driving, I'll have to take a listen after its been sitting for a while.

If it is indeed the A/C compressor making this noise, I assume its nothing to worry about?

 

Yeah! - I would not loose sleep. Refrigerant can remain mobile for quite a while after shut down - it's ambient temperature related so I don't want to guess how long. Listen to the car after it's been shut down 4 plus hours & see if it still makes a noise. You are not the first one to report this but it's never really been resolved on the forum.

 

As long as its not leaking out of the system, its alright with me!

Thanks for the advice.

 

Nothing to worry about, it is indeed the AC equalizing.
Does the noise remind you of an old dot matrix printer?

 

Yeah, it's a little like that, but not quite as harsh sounding. (Our old dot matrix printer at the speed shop was pretty loud and noisy)