I replaced the idiotically loud motherboard fan with a 24V 40/10 Noctua. It needs slightly longer screws than the stock ones but otherwise it's a drop in replacement. Noise levels are much more acceptable now.
I've been doing some light research and i think it's possible to run the stock fan slower and turn it off when not printing, but it's unclear whether i'd have to plug the fan into a different header or not.
Because the full info is in a private facebook group :bleugh: