99 ml320 has a exhaust type noise (ticking) only when truck is under load, as soon as I take foot of gas no sound. Idle is ok no sound, performance is normal. Only hear the loud noise when windows are down, and gets louder if a car, wall, curb is on ether side of truck.Went to muffler shop and he said system is good. Maybe exhaust manifold. Any ideas? How do you check the manifold? Thanks for your time...

 

Hi Buzzbe,
is that noise there only when car is moving? If you rev the engine in park or neutral can you hear that noise? If it is not present standing still, your problem could be driveshaft center support bearing described a couple threads ago. There are some cases with cat. convertor problems by I think the muffler shop would of found it. How many miles on it?

 

if I put my foot on gas and brake at the same time I can reproduce the sound standing still. If I rev the engine in park or neutral no noise! 140k miles on suv.

 

That says at all. You have no engine noise, your engine is fine. If you have to have gear engaged in order to hear it, I believe that it's coming from your transmission. I bought my '99 ML320 at 130K with broken tranny. Go back couple of threads here in M-class or to E-class, 3 days ago I was replying to transmission fluid check and replacement. Do check it, it is NOT a "lifetime fluid fill" as Mercedes was claiming in manuals reather "warranty over fill" because now they have changed their minds about it on newer versions then ours. Did you ever changed the fluid and filter in it?