I oil my fans when I'm going to install them (most of the time). If they are new I may not.
I peal the sticker off,
drop in a few drops of 3-in-one oil on the shaft,
work the fan a little back and forth, add more oil if it will take it,
reseal the shaft with "FOIL" duct tape.
Just make sure and clean all the oil of the fan surface, so the "FOIL" tape will seal properly.
I've help quiet down several fans this way.