Strange noise after oil change...

Hello!

I've also heard this noise after the last oil change, and I can definitely identify its source. It's a blow-off valve from the turbo.
But where does that come from in the case of the VTG Turbo?
So, I went on a search today.
Here's the translation:

"I need to preface this by saying:"
The noise only occurs within the range of approximately 1500 RPM when I release the accelerator after a brief burst of acceleration. At higher speeds, I can't hear or reproduce the noise.
My first suspicion falls on the throttle valve. I unplugged the connector, and... the noise disappeared. The door is held open by a spring mechanism, so it remains in the open position when there is no power.
But why is the turbocharger whistling even when it's being controlled correctly?
Next attempt using the .019CR software (which is glitchy). Here too, the whistling can be observed, but now it can be traced up to almost 2000 RPM.
"Since I am aware that several changes were made to the AGR parameters in the 019MQ software, I assume that the DK (diesel particulate filter) is closed during the torque cutoff (at least up to approximately 1500 rpm). After conducting some measurements on the DK while driving, I can confirm this." At higher speeds, the diverter valve closes slightly delayed to allow the turbo pressure to decrease first.
Now I understand why my AXR runs so smoothly, even with the turbocharger shut off (with almost zero braking torque). The diverter valve is closed, so the engine doesn't need to do (or very little) compression work. This promotes an extremely long rolling distance.
Why do I only notice the noise after the oil change?
Okay... the engine is quiet again now, so I can hear those small, subtle noises. For the last 5-7,000 kilometers, the engine had been extremely loud. The noise is definitely always there.

I learned some more about the quirks of my AXR.

Perhaps the turbo is happy about the fresh oil and is therefore making a cheerful sound. In any case, I've noticed several times that my cars have sounded different after an oil change, at least initially. However, it always subsided quickly.
I think that the new oil will quickly thicken again or have its viscosity altered due to the residues that remain in the engine.