In many cases the fans that are used for the cooling of copiers and computers can get very noisy. The simple solution is to just replace them but if you don’t have the money then there are two solutions.
1. Get an old tooth brush and clean the blades. Unbalanced blades can make a lot of noise.
2. Get some oil, 3 in one is best but in a pinch wd40 will work, and take off the silver tab on the back of the fan and grease the fan bearing. Then glue back the tab on and you are good to go.