@Marius-Breuer note further on in the Noctua white paper - "External pull-up is not necessary as the signal is pulled up to 3,3V/5V inside the fan."

However, Noctua also deprecates using a single transistor and relying on the pullup and favours a two transistor drive circuit for the PWM (also further on in the white paper). I have found with some fans a need to add an additional external pullup, and actually I've generally pulled up to 12V (though not with a Noctua fan, and I note they say don't pull to 12V) see e.g. https://forum.duet3d.com/post/306593.

This is covered at https://duet3d.dozuki.com/Wiki/Connector_and_spare_part_numbers#Section_Blade_fuses.

@Jim46 it is really quite nice and thermostatically controlled as well but you would have to remove those heatsinks!