If I have posted this again, forgive me. I could not find any information on the subject from before. I have 90 420sel (w126) that at 110k had a timing chain service done. I now have 116k on it and all of a sudden have developed a strange noise or pop. After driving, I pull into a parking place and put into park, but leave the car running. With the window down, once about every 1-2 minutes you can hear a pop-like noise that seems to come from underneath the car. It is fairly loud and is only a single pop. I think I emailed someone on this once and got some information, but can't remember or find the response. The pop sounds almost like you have taken a hammer and hit a piece of thick metal. It does not echo like hitting metal does and it is a very short destinct pop. I have even noticed it happening once I have turned the car off and have gotten out and shut the door as I am walking away from the car. You can sometimes hear it then until the car has cooled off for a few minutes. Could this be something to do with a heat shield or something that heat effects? If it only did it when the car was running, I would think it was something in the motor, but it has done it a few times after the motor has been turned off. Any help you can give me would greatly be appreciated.

I would check catalytic converter, resonator & muffler, for expansion/contraction .
The temperature of these components will drop very rapidly after a drive, even when you come to an idle.

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2007 C 230 Sport.

Manny, can you give me some details of what you are thinking? When you say expansion and contraction what exactly you mean of this? Is this normal? Is this bad and can it mess something up? Thanks for your help.

Next time you get home from a good drive, either shut off the engine or leave it idling.
Then quickly look & listen under the car for the noise you describe.
I think you are hearing a shrinking/popping /cooling down, from an exhaust component.
A friend of mine's vehicle used to do this.
Turned out to be a seperated baffle in the muffler.

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2007 C 230 Sport.

Thanks Manny for your help. Is it possible to hear this pop not only on the outside of the car, but once in a while it gives me the impression that it also sounds through one of the speakers inside. Maybe the noise is so loud that it just appears like it comes through the speaker. If it turns out to be that separated baffle, is the only way to fix it by replacing the muffler and is it dangerous to run the car with it doing it. What exactly did your friend end up doing to fix the problem? Thanks again. Board members like yourself are great to talk to. Scott

There is nothing dangerous about any of it.
My buddy ( not a Mercedes ),ended up with a new muffler.
Just check it as I said.
May want to use a flashlight but, listen for the direction where the noise is coming from first.
I can't see it having any effect on your speakers.

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2007 C 230 Sport.