Tack Noise in Sliding Doors

Hello, experts in engine acoustics!

Perhaps I'll hear the fleas coughing or the grass growing again someday, but in any case, I haven't really been enjoying the sound of the engine lately.
The aforementioned AGR (Abgas Rückführung - Exhaust Gas Recirculation) system sounds somewhat more robust than comparable units, as it neither ingests exhaust byproducts nor suffers from diesel buildup in front of the injector nozzles. Furthermore, the opening pressure of the first stage is set to 220 bar instead of 190 bar.
Besides the slightly louder running noise caused by this, there are other noises that seem a bit unusual to me.
Specifically during operation in the "glide" mode, between 1500 and 2200 RPM, one can hear a knocking sound that doesn't sound healthy at all. The sound of the fuel injection system can definitely be ruled out in this case (glide mode!).
Could those be the lifters? Is this the beginning of a connecting rod bearing failure?
IMO, faulty hydraulic lifters tend to sound "brighter" and more like a ticking noise.

Oh, I had the feeling that the engine sound changed after a brutal highway drive (I was really in a hurry -> due to time pressure). The engine was running between 4200-4700 RPM for over 1 hour. It really ran great, but subjectively, it sounded a bit more metallic afterwards .

Thank you for your help.

Regards,
Alex.

Hi Alex,

Could it be that these are what are known as 'piston-tilters'? In this case, the piston could tilt slightly within the cylinder, relative to the connecting rod.
I seem to recall reading something about how this kind of noise can be heard especially during the 'throttling' phase, because there's no pressure in the combustion chamber at that point that would normally prevent the valve from tilting.

Or does it simply sound original again, having burned off a lot of dirt and deposits?

Greetings.

Eike.

I think I recognize that sound, as my ATJ also has it (if it's the same thing). However, it always occurs in my case.

This sound is like a snore and it sounds like metal rubbing against metal.

Best regards, WarLord.

Hello everyone!

I took the time today, after work, to remove the upper engine cover. Then, I let the engine run in neutral and used a long screwdriver (stethoscope kit ) to listen to the engine.
Due to the limited space available, I was only able to monitor the area around the central unit. However, I didn't notice any unusual noises.
Interestingly, I could perceive unpleasant noises during the ride .
I think the engine is making a noticeably louder knocking sound during the warm-up phase than it was a while ago. I also believe I'm hearing an irregularity that seems to be coming from one of the cylinders.
Yesterday, I read the MWB13 data, but there were no indications of any irregularities. The deviations are less than 0.2 mg/H.

Does anyone have any other ideas ?

I don't want the engine to suddenly fail on me. Besides, a bearing problem in its early stages can still be easily fixed without damaging the crankshaft and/or connecting rods.

What about hydraulic noises, such as those caused by a lifter that is sticking intermittently? Could that be the cause of the knocking sound?
I think I'll take off the valve cover this weekend and take a closer look at the camshaft and the hydraulic lifters.

Regards,
Alex.