74styles,

I also notice some noise coming from the area under air pump. It's faint. I thought it's a lifter noise at first. It sounds like semi-defective bearing noise when rollers are out the holder. I can also call it marbles in a can sound. If I put long screwdriver to the engine and put my ear to the handle, the noise will be the loudest around air pump area. It seems that the noise is coming from inside the motor. Air pump only runs once in awhile, during initial engine start in the morning and when you get off the highway. It doesn't run all the time so I cannot be noise source. Maybe it's timing chain noise? I change oil and added 2 bottles of Lucas additive and I can say that my noise quited down along with lifter noise. Lifter noise during cold morning start is gone completely. Did you find a source of your noise?

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1999 ML430 Silver 135k ml
Smoked LED taillights, Alpine in-dash DVD player, 12" sub, Pioneer components, 2 amps, 4200k HIDs, ML55 headlights, 20" rims, mirror LED blinkers

SOLD. 1996 E320 145k ml. Burgundy

SOLD but miss it everyday 1992 500sel Black
Chime buzzer mod,Alpine CD/MP3 player with stock amp,Euro headlights,S600 grill,20" rims, BEST CAR EVER!

SOLD. 1990 300E White
187k ml,smoked tails,Euro headlights,17rims,Intake,12" sub in first aid kit,alarm/autostart,buzzer mod