Hi Razvan...welcome to the Forum
Difficult one to pinpoint the cause ..... first thoughts were of the turbo bearings failing but not so sure as it only hits the spot at certain revs and it was bearings it would evidence throughout the rev range.
Thinking it may be an induction leak (inlet manifold, hoses, intercooler, etc) but don't discount an exhaust leak (anywhere from the manifold, turbo and through to the downpipe).
Maybe a smoke test is the best way forward....that would narrow down the possible causes almost immediately.
Let us know what you find
Cheers, Trevor