@catterfly do you have an aerosol duster? blow that in the vent and it'll probably quiet down; it's likely it's just got dust stuck in it that's making it have to work harder
@catterfly probably a good idea, yeah, or maybe some dust or a hair or something has managed to get tangled around the fan bearing or something. Probably an easy fix.
Well, not so easy if the fan blade's snapped, but still, replacing a fan is not the most difficult thing in the world.