Most ceiling fans do not have a way to libricate the motor or bearings. You usually get the sort of noise you describe when the fan is not properly balanced. Does it wobble when running? Is it connected to a sturdy box at the ceiling, or does it wiggle at the top too? It should be sturdy and stationary at the top, and then the blades should be balanced. You can get a balancing kit and instructions where they sell ceiling fans.
If nothing solves the problem, you'll probably have to live with the noise or replace the fan.
ps. WD40 is not a grease, and not a particularly good lubricant. (It wasn't designed to be a lubricant.)

[This message has been edited by rpxlpx (edited February 07, 2001).]