CentralFLBenz

I have a 2007 Mercedes E350 with 108k on it and it's currently in a repair shop and they are having a hard time figuring out what it is. Usually makes the noise in 30 second or less intervals and always under 2000 rpm, very loud howling noise from inside the car but pretty sure it's coming from the engine. I recently changed out the serpentine belt and all the pulleys hoping that was it. Any ideas? The sound actually went on for another 20 seconds but I had to shorten the video to get it on here.

CentralFLBenz

Car has been in the shop 3 days now and they still cannot figure it out.

RCPDesigns

Is the noise related to RPM? (faster/slower RPM changes pitch or loudness of noise)

Playing back your video it sounds like a tone generator... is it coming from the sound system?

I know my E350 doesn't have air suspension but maybe yours does... if so, it might be the air compressor for the air suspension.

The sound is also similar to valve flutter (not the intake/exhaust valves). It could be a valve and/or pressure regulator that is switching rapidly open/closed at a rate such to generate the tone you hear. I would assume the air conditioning system has such valves. A severely restricted valve (pinched tubing) might generate the same sound.

CentralFLBenz

Thanks for the suggestions, I'll pass it on to the shop and see what they say. We're on the 4th day now trying to figure it out.

LILBENZ230

The E350 does not have air suspension for sure.

I agree the video is not really enough. To my on my end it sounds like it is coming from the sound system, but I'm sure you would know that right away.

CentralFLBenz

Well after 4 days they could not pinpoint it so after a brake flush I took it home. Surprisingly the whole way home it did not make the sound. They think it's possibly the AC compressor and told me if I hear it to turn the air off and if it stops that's most likely it. The warranty I have covers that so we'll see. Might just be one of those fluke things.

CentralFLBenz

Well it's the AC compressor, when I turn the air off the noise goes away. Luckily the warranty I bought covers this so glad to have figured it out!

cMazara

Wished I had warranty !! Glad that you found out what the problem was.

CentralFLBenz

Thought I would post an update in case this happens to anyone else...So after the AC compressor was replaced we thought all was well and of course the noise came back. The shop said bring it back and they replaced the AC expansion valve and that fixed the issue, cheap part but a couple hours labor at no cost to me. Glad it's FINALLY figured out.