If cleaning hasn't solved the problem and the blades are not brushing against anything, see if the fan is firmly attached. If it's screwed on, check the screws. If it's still not that, peel off the sticker and apply a small gob of grease on the bearing or bushing.
If that does not cure it, it's time to replace the fan. Even if you can live with the noise, it's probably nearing the end of its useful life.
Some noisy fans can keep on working for a long time, but since it's a P-3, it's probably quite a few years old. And it may stop or slow down too much to give adequate cooling without your noticing it, and your processor will be fried. Fans are much cheaper to replace.