It is the cam advance part. Not sure what it is called, but it has been mentioned on other forums. Since the M111 2.3 engine has Variable Intake Timing this unit makes some noise sometimes. My M271 does some what the same thing. For the first 1-2 seconds after starting I can hear them! It has done it since day one on my 2003. And after 42000 miles it still does it and I have never had any issues.

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~Jamie
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2003 Pewter C230K SC C1, C4, C5, C7, heated seats, CD Changer, and 6 Speed. ContiExtremes on the C7's.

1986 190E 2.3 Black, Auto, Mods to come soon.....