doesnt seem to be lifters,have tried diff oil,when I loosen inj line on 3 or 4 it quiets a little,NOT a rod knock,Seems to be maybe a weak or broken spring in the injector,Just fishing kind of,I have put about 6000 miles on this car,No change in the noise,no change in performance,pretty consistant knock at idle,just seems a little loud for this car. I may pull apart those injectors and have a look,remans from mercedes are only $42.00 ea so maybe just change em. Are these motors normally quiet at idle say compared to a 617 series,just sold a 123 sedan that is Much quieter than mine but not nearly as peppy on the road.