A3 - AHF: Humming at 2000 RPM

Hi!
So, bei meinem A3 mit 81 kW und 150.000 km (AHF) verstehe ich nicht wirklich, was ich erwarten kann. Wenn ich meinen A3 mit dem A3 meines Kollegen beim Beschleunigen vergleiche, komme ich ihm nicht wirklich davon . The problem is that there's only one 66kw engine inside. Well, the mileage is pretty much the same, and the equipment, i.e. the weight, is definitely not very different.
I've just checked my AHF and, as far as I can tell, there are no problems. The AGR has been cleaned and deactivated (metal). The O2 sensor was evaluated as being in perfect condition during a test drive (VAG-Com). The VTG - adjustment also works perfectly (no clicking or other issues). Air filter, diesel filter are new, fuel tank vent is clear, LLK is verschandeln and hoses are sealed.
BUT: If I rev the engine properly, the engine noise changes around 2000 and then it starts revving normally again around 2300. There is no jerking or other loss of power. Just this slightly louder engine noise (rumbling).
Furthermore, I suspect that he doesn't have the necessary power in the 4th and 5th gear, as he should. The top speed is also reached, and the fuel consumption of 5.6l is actually quite good. (more suitable for long distances)
Could this humming or slight power loss also be due to worn-out injectors? Especially since I think the previous owner used biodiesel. Because I also had to replace my fuel pump about 30,000 km ago.
Or could this also be due to the turbo? My oil consumption is around 2 liters per 15,000 km, which is not alarming, but it could be due to the turbo. (Lots of highway driving at around 160 km/h)
Maybe someone has suggestions or has had similar problems. In the search function, I have already read a lot about performance loss and fuel injectors, but most of this doesn't really apply to my vehicle.
Best regards