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2010 C300 hissing noise sound at 30 mph+???

3K views 2 replies 3 participants last post by  William Alexander 
#1 ·
1) 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 gets much louder when the ashtray is opened. It's like a "shhhhhhhh" sound. 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???

2) Unrelated to the first issue, but the fan blower settings, when it's around the 4th or 5th bar for fan speed, it sounds a little whistlely, very slight, barely noticeable. Didn't know if that is normal. I can hear it louder the closer I put my head near the passenger side floor.
 
#2 ·
Hey, Just thought I would write in to let you know my experiences. I have a 2008 c300 4matic.

I too had a hissing noise which sounded as though it was coming from behind the thermostat / ash tray. It was only present when travelling, and as you say, got worse with speed (over 30mph).

I looked around and saw some posts about a brake booster, and one other issue - and asked my dealer multiple times to look into it. They said it wasnt a problem with either and gave valid reasons as to why.

I took it in one last time and was told it was a bearing that was wearing out in the transmission. They replaced the transmission, and what do you know? The noise is gone.

My warranty had run out in march, and I just got the car back. Fortunately, I had picked up the extended LIMITED warranty which covered this repair. It did not, however, cover things like the lights being out in my ash tray. (just incase you ever consider the warranty)

The way they said they ended up diagnosing it is by using "chasis ears" and pin-pointing the exact location, however, on my test drive with the shop foreman, he had a good idea as to what the noise was.
 
#3 ·
Strange that a 2010 would have this transmission problem, as nearly a million W204's were produced by the end of the 2010 MY. As for fan noise, make sure nothing obstructs the ventilation system intakes and also open all your vents including the rear passenger vents if you are running the fan at 4 or 5. The W204 ventilation system is supposed to be 3dB quieter than the previous model, however these are designed to be quieter only with all vents fully opened.
 
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