JeruC350

Hello all. I've recently noticed an audible noise that occurs immediately after coming to a complete stop. I've tried to figure out where the noise is coming from without success. It's a single knock/tap sound that seems to come from under the car, possibly toward the front. I've had a dealer look into it, both the SA and mechanic heard the noise but couldn't identify or rectify the noise. We took a ride in a 2008 c350 off of their lot (identical to my car in every way other than color) and it made the same exact noise as my car when coming to a complete stop. They ultimately chalked it up as a characteristic of the car. I'm not convinced that is true because I've owned my car for almost 2 years now and I'm almost positive I would have noticed that noise if it were always there. However, now I am doubting myself because what are the odds that their car just happened to have the same exact problem as mine? I am very OCD when it comes to noises and just cannot believe I've missed it for all this time. Has anyone here experienced the same noise in your w204 or happen to know what could be the cause? It is just a single knock/pop after the car stops completely and that is the only time it happens. It happens every time I stop after driving above 40 mph and comes and goes when stopping after driving at speeds below 40 mph. Thank you all in advance for your help.

JeruC350

Anyone?

italiasix

JeruC350, my car is doing the same exact thing (I have a 2010) and it only makes the noise after you have gone through most of the gears (i.e. 40mph) and what I have fig out was it is definitely coming from thetransmission. The reason why I know this is because, I put the car in neutral and rolled to a stop and I did not hear the noise. I plan to take it to Mercedes and see what they have to say? Did you get your issue resolved?

italiasix

JeruC350, my car is doing the same exact thing (I have a 2010) and it only makes the noise after you have gone through most of the gears (i.e. 40mph) and what I have fig out was it is definitely coming from thetransmission. The reason why I know this is because, I put the car in neutral and rolled to a stop and I did not hear the noise. I plan to take it to Mercedes and see what they have to say? Did you get your issue resolved?

JeruC350

Unfortunately no. Im still trying to figure out whats making this happen. Ive been told 2 times by the service dept at my dealer that the noise is normal. But I know its not. https://mbworld.org/forums/showthrea...522&styleid=18
Check out this thread.. it has all the info ive come up with thus far. I hope one of us finds a fix soon. It is so annoying.

JeruC350

Please Italiasix, let me know if you find the solution. Im dying to get this fixed as im sure you are as well. I plan on taking my car to a benz specialist in my area as soon as I can afford it. I promise to post a diagnosis/fix if I come up with one. Thanks.

johnmartin

Hi guys,
Im experiencing the same problem. The knocking sound seems to be more noticeable in the cabin passenger side (LHS). If you have resolved this issue please let me know.

xijonix

Not too much that could make a single clunk like that, could be any number of things

Sway Bar End Links
Ball Joints
Loose Strut

In some cases may be related to front brakes where pads shift.

fahad4890

I've had the same noise. I bought an '09 C350 sport back in November, I researched it and have been fairly indifferent as the car was CPO and was inspected by my mechanic. Test drove the crap out of the car. I have heard it in other C Classes as well.

2006_C350

I have the same problem, car is 2010 C300 with about 31K miles when this sound started. My car is almost out of warranty and it's going in for service soon. I need help because last time the SA and tech said it is normal.

tpdietz

I had this problem. Try this to see if it replicates the sound you are referring to...

With your engine off, open the hood. At the passenger side, near the dash you will notice a black box with some clips that can be easily removed by hand (no tools). This box helps directs air into your car. Once removed you should see a mechanism that blocks air flow, but can rotated downwards to open air flow. (If your engine is running, this mechanism will be open) This can be moved very easily by hand, not much resistance but some. This is the mechanism that will close if you push the circulate button on your climate controls. Now go sit in your car with the engine still off. Have somebody manually open the mechanism, and once fully open have them release it. This spring like action will cause a thud when the mechanism resumes the closed position.

EDIT: I had this backwards. By default the mechanism is open. You should close it, then release the mechanism and it will spring back open. See pics in my other post.

Is this the noise you where hearing? It was for me.

Good luck!

2006_C350

Can you post some pics?

tpdietz

Below are pictures. You can see how I reach in, pull the mechanism down, until it closes completely. Once completely closed, let go and it will pop back open, creating a thud.

This was the noise I was hearing when coming to a stop. Sometimes it happened after I stopped, or when I was close to stopping. Usually after driving at highway speeds.

EDIT: I was incorrect earlier when I said this would be closed when the engine is off. Notice it is open by default. Be sure to have somebody else do this for you while you are in the car. The noise is different from inside the vehicle.

2006_C350

When I am in gear going 40 MPH per hour and coming to a complete stop I hear the popping noise. When I put the transmission into NEUTRAL while going 40 MPH and coming to a complete stop there is NO popping noise.

I tried this exercise several times.

My car is almost out of warranty and I hope it's not a sign of a tranny problem. I would at least like it to be documented by Mercedes.

Can anyone chime in?

2006_C350

The dealer says it is probably the rear engine mounts AKA the transmission mounts. What's the consensus on this diagnosis?