Golf TDI: Turbo Whistle in Partial Load?

Hey everyone!
I've noticed that my car sometimes makes a whistling or whooshing sound, especially when I release the accelerator pedal, particularly at lower engine loads. It's kind of like a loud, drawn-out whistle.
It occurs both in warm and cold conditions! It happens less frequently in warm conditions!
Also, here's the translation:

'It also happens repeatedly with the same pedal position!'
The performance is normal.
I'm wondering if this is something I should be concerned about.
People are just staring blankly! It's really loud!
Is this a 90 horsepower engine (1Z)?
Thank you for the tips!

Hi,

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Best regards, Rainer.