I volunteered at a university radio station a few times and was taught how to cut out AC/Heater/Fan noise from a recording using audacity on what I think was my second time going in. Recorded a PSA about cancer screening.

It’s been almost a decade and a half so I don’t remember exactly how, but the point is that it was something they taught people effectively walking in off the street.

I’d imagine it’s different with a non-constant fan, but you can force computer fans to a consistent 100% speed through a handful of different ways.