Audi 80 B4: Knocking Z1 Engine - Diagnosis & Repair

Hello there.

I have an Audi B4 TDI.
"Since I drove 2000 km, I've been experiencing a knocking/clicking sound, but only when the engine is cold and at speeds above 90 km/h."
It's coming from the cylinder on the vertical wall or from that direction.
My guess is either a vacuum pump or an injector nozzle.
Who can give me good advice?

Thank you in advance.


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