How do I quiet noisy computer fans?

I'm sorry to say the best solution is to replace the fan. If you are on a budget or are working with legacy components that can’t be replaced, you can try to lubricate the fan. DO NOT use WD-40, it is not made for high speed motors and is flammable. I use 3 in 1 motor oil, a small bottle can be had at any hardware store. For the more adventuresome types, sewing machine oil is an excellent lubricant for fans and can be found at most fabric stores.