Turbo whistles after a visit to the workshop

My 2.7 TDI (engine code BPP) has had sluggish throttle response in the lower RPM range, up to approximately 1800 RPM, since I bought it as a used car.
With the tuning from MTM, it became even more noticeable.

"For a few years, I thought it might be related to the large turbocharger. But last year, I noticed that when I really pushed the accelerator around 1400 RPM, the power delivery felt very sluggish. However, if I let off the gas and then quickly accelerate again, the engine revs up well."
You can also notice that when you ease off the gas, there's a point where you experience a sudden acceleration surge. If you then gradually increase the gas again, the acceleration is noticeably higher than normal.

I suspected that the VTG shaft might be too short (the engine has an electronic actuator, and the shaft is not adjustable), so the electronic actuator might not be aligned correctly with the turbocharger in terms of its rotational position.

In short, I then took it to the workshop.

When I picked up the car, the turbo suddenly started making a very loud noise. However, it hadn't been making that noise during the test drive with the mechanic.
The sound isn't really a whistle, more like a hum. When the full boost pressure is reached, it sounds like a bright buzzing or whistling. It doesn't change throughout the entire RPM range. Overall, it's noticeably louder than my radio.

Allegedly, only an actuator diagnosis and a fault diagnosis program were run.

But honestly, this kind of effect, the damage comes slowly and not suddenly.


Could the effect be due to the turbocharger (e.g., bearing play), or are there other possible causes for the turbocharger noise?

What could have caused the damage?

I've now removed the intake manifold. The housing around the first compressor wheel is slightly rough, and the shaft has radial play.
Normally, that should only be a few hundredths, right? It seems more like several tenths to me.
The flange at the compressor outlet is also very oily, and the engine oil level was also at the lower limit.

The wave seems to have subsided. But still, does that whistling suddenly appear?

Could there be another cause?

The turbo has been replaced, and the old one has been disassembled.

A small corner of a blade had broken off the gas turbine.
Interestingly, this occurs at the end, where the diameter is smallest, and therefore the centrifugal forces are lowest.
However, at that point, the runner wheel is already entering the exhaust pipe, and there are deep scratches and a bent deflector plate.

It looks like a foreign object passed through the turbocharger.

Could this be related to a spark plug replacement done at the workshop?

The expert mentioned that there were cases with the 2.5 TDI engines where parts of the air-gap insulated manifold had broken off. Apparently, this also occurred in some of the 2.7 engines.

The cause could be... you should simply check what's lying around the cat. Everything else is speculation until you find something, if you find something .

Good idea.
It requires some effort on my part, but it should be worth it.