Knocking noise while idling on 2002 Mercedes-Benz C230

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Hi I'm wondering if anyone has any advice or experience with a knocking noise that happens during idling? Anything will help Thanks!
(1) Answer
Be sure your oil level is full first. check to see if the oil light is on or pressure if gauge is up to normal level. Try to determine if the noise is coming from the bottom or top of the engine. Rod noise ( bottom ) will tend to be steady beat that will stay about the same as engine speed is increased. Lifter noise ( top ) will have a tap that increases as engine speed dose, will sound much faster then at idle. There is a lot of reasons for this and all need attention soon. Hope this helps you for now.