well, my 93 had a tick like that, I can't remember how intermittent it was though, I think it was worse hot. But in the end it was lifter tick due to oil pressure to the head. I replaced all my lifters and it still ticked after that (I don't think they needed replaced). I kept driving it with the tick. Eventually my head gasket blew, the gaskets on theses engine will push over and block the oil port that feeds the head and block oil flow thus lowering oil pressure to hyd lifters. They push between the number 1 and oil galley. I would tend to bet it could be this. If this is indeed happening you want to catch it before it blows because it can damage the aluminum head by gouging it at that point, that's what happened to mine. Anyways if you think it is an internal knock like that and not a fueling knock I would just do a head gasket. I believe there are other post on this problem try searching it.

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2005 e320 cdi (132,000)
2005 Jeep CRD diesel--2.8L (138,000 miles) wrecked, insurance took
1993 Mercedes benz 300D 2.5 Turbo Frybrid powered. (336,000 miles) wrecked and sold as parts car
1990 Mercedes benz 300D 2.5 Turbo (170,000 miles) wrecked and sold as parts car

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