Just sharing some thoughts and my own theory on the Noctua fans.. You should be buying the 4pin noctua A4x10 PWM version of the fan.. looking at the circuitry diagram below, the yellow cable in the 3 pin version is RPM speed signal and not PWM signal.. The PWM signal cable is carried in the blue wire on the 4pin version..
So, you need to buy the 4pin version and map the wires like this to the original fan adaptor:
- Noctua Blue > Original Yellow
- Noctua Yellow > Original Red
- Noctua Black > Original Black
- Noctua Green > (to cut away)
Following the above rewiring, you should be able to achieve PWM speed control..
