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Hi all,
When starting up, I have a noise coming from my engine compartment which sounds like a clicking or ticking. It goes with the RPM and has something of a diesel-y sound to it. When I open the hood to listen, the regular noise of the engine drowns it out. I figured this wasn't too big of a deal since it was just on the cold engine, but now it's begun to remain throughout the drive and is becoming louder. What are some things I should look for? Perhaps a pulley, the oil or the water pump?

Potentially unrelated, I had to add coolant recently. Perhaps a slow leak at the water pump, but I haven't added or changed coolant for 1.5 years.

As always, thanks for the help!
 

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Could be alternator, aircon compressor, Kompressor, water pump, valve, etc. Get a mechanics stethoscope from Harbor Freight for about 5 bucks and you can track it down.
 

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Hello, I am no mechanic but what you have described sounds like the problem I had last year. When I first took it into the garage they could find nothing wrong, but the noise became more frequent, and got louder, and in the end sounded like I was dragging tin cans. Boyfriend popped the bonnet with the engine running and noticed that one of the wheels would stop and restart - turned out this was the supercharger clutch, so had it replaced.
That said, my car is the R170 which had a known issue.
 

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Similar Problem

Hi have a 2003 R170 with a similar noise I think. It's a rattling or perhaps a vibration at startup and when the engine is cold. It got REALLY bad on a recent trip and seemed to coincide with a slow leak/low level in the coolant. When I got home I changed the water pump. The noise improved SIGNIFICANTLY but it's still there.

It only happens when the car is cold. After warm up it seems to disappear. It also disappears at low RPM < about 1500 and disappears again at high acceleration/RPM > about 4500. The "sweet spot" to make the noise seems with a cold car between 1600 and about 3800 RPM.

Is it possible that there may be an air bubble in the coolant and the noise is caused by the pump running dry?? It irritates me that you can't fill directly into the radiator on this car and only into the expansion tank. . .

Anyone have any thoughts? Am I on the right track?
 

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Hmmm.. can it be the harmonic balancer or idler pulley?! Try to visually inspect pulleys and see if any of them are wobbling.
When I changed my coolant or when my coolant tank was leaking I used to top it up with some coolant and squeeze the big water coolant line on top several times with the cap still open, and you can hear "swoosh swoosh". This will force the air out. But if any bubbles are left it should come out via a venting whole so shouldn't be an issue with Mercedes.

Another thing you said you have a vibration... Is it like resonating and appears only at certain RPMs?! I'm saying it because it might be bad engine mounts. At least that's how my symptoms were. A resonating vibration sound that was hard to my ears at certain RPMs (think it was somewhere between 1500-2100). Replaced the mounts and was gone. Turned out one side gave up and I was able to squeeze it with my hand. It wasn't leaking though... So worthwhile to be checked.
 
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