skytom88

I went to the Benz Dealer yesterday to fix some problems.

One of them was a hissing sound from the engine.

When the engine is on and I'm driving, there is a hissing sound. It sounds as if I have a speaker on but without any music coming out of it.
When I hit the brakes, the hissing sound goes away. The harder I press on the brakes, the sound disappears. It sounds like I am "controlling the hissing volume" with the brakes. (If I press on the brakes really softly, the sound becomes really minimal.)

The service rep. said this is the sound of engine pumps running and that it is NORMAL.

When I got a 2010 C300 loaner car, it didn't have this sound...

So... anyone know if this is normal or a problem?

Thanks a lot for you guys' help!

Savage c-300

I remember having this issue and the dealership had to replace some hose. It's not normal.

hitokiri89

That sounds dangerous I would take it back to the dealership

RLE

It's obviously a vacuum leak. Here's another example of uninformed service writers trying to BS customers with standard answers that they learn in SA school.

Talk to the Service Manager.

skytom88

i knew it!! okay. thanks for your input. This sound wasn't there when I first got the car and it's just 1 year old!

chuang

Were you able to confirm that it is vacuum leak problem?

My 2 weeks "brand new" 2012 C250 Sedan also have a weird hissing sound coming from the engine when idle. Here is the sound clip recorded by my android phone:

http://yourlisten.com/channel/conten...n=8cjeoqorhrwg

Does anyone know what problem this may be? Does this sound like vacuum leak? Thanks!

C300Sport

God don't you hate it when the "it's normal" BS comes up when you just want to get something fixed.
You may want to remind them that if you end up plowing your car into something because of your obvious vacuum leak, MB will be taking care of you for life...hate lawsuits and the threat of them but a reminder of this potentially being a saftey issue often does grease the wheels.

C300Sport

Is that a squeak or a squeaky sounding hiss? Not sure what it is but it's not normal.

bigigg

Make sure all hoses are properly connected to the air intake box.

Jason B

I have a sound like this on a 2010 c300. It's like a hissing/static sound above 30 mph and gets louder the faster you go. It sounds like its coming from the middle of the dash area. Braking doesn't effect it and I even put it in neutral at 50 mph and shut the engine and radio off while coasting and it's still there. Ideas???