[maslin]

I am a master tech, have been since 2012. With Mercedes, but engine technology is pretty much the same across the board.

First thing I would do is attach the NVH kit with a Picoscope and go from there.

Is the noise metallic? Then it’s something metal. Only under load or when you lift off? A deep duka duka duka is from the bottom end, pico will point our main or rod bearings. A more frequent rattle is usually wrist pins, not a hollow sound. Piston slap sounds like piston slap, usually a little tinnier.

Or is it an air noise, compression or leak? Possibly fuel? High pressure pumps can click, not just chirp.

It could be a ton of things. Noisy valves are usually worst at idle. Noise from the timing chain is sometimes only evident at start up. Etc etc etc.

Sucks the dealer can’t get to a conclusion, hopefully it isn’t pushed in a corner collecting dust while they’re “working on it”.

Edit: I’m not trying to be obtuse. Engine are engines. They make a noise, 10 seconds in you have a general idea where to go. A stethoscope will get you tot a general area very quickly. It can be more difficult when it only occurs under load, but there are means to every end. Seems like the question of “who’s paying” might be the biggest hurdle at this point, I just find it so hard to believe these dealerships aren’t taking care of an issue that occurred shortly after having an engine out and 80% torn down.