The 30mm fan that is used for the PCB Effector from T3P3/Escher3D is way too loud for my taste.
Fitting a 40mm fan duct in the narrow space when you also use the parts cooler can be problematic. So I designed the following angled fan duct that seems to work fine.
edit 171016: added a version with the fan mount part thinned about 2mm. Not tested/printed by me so I don't know it it will work. But I don't see why it shouldn't.