Mysterious Rattle on start up


Senior Member
Oct 2, 2012
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Your Mercedes
E 250 cabriolet, 190E 2.0L

I have a 2010 Om651 powered E class with 110k miles on it that occasionally rattles (a slow ticking noise) on starts. The noise sounds very different to the chain noise I've seen in videos of worn/stretched chains. I changed the timing chain, sprockets, tensioner etc with OEM parts about 6 months ago just to be safe but the noise is still there.

The rattle is intermittent and occurs randomly without any pattern. Car can sit for a week start with no rattle then rattle on the next start 10 min later. Its random and not only on cold starts. It never does it in front of a mechanic so I've never been able to demonstrate it. The mechanic who did the chain job even said the original chain parts didn't actually look bad and the chain wasn't stretched more than you'd expect from the milage.

The noise is only audible for 1 or 2 seconds from inside the car however I've noticed the noise can be heard continuously (albeit much quieter) when kneeling next to the rear wheels at idle. It sounds like it's coming from underneath near the center or rear of the car rather than the the engine itself.

Could it be the exhaust that rattles and is louder on starting? The noise at idle sounds exactly the same as the noise at startup but quieter.

Engine runs well with no faults or dash lights. Any ideas to this mystery?

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