It might help a little to find out whether the noise is coming from the wind being blown by the fan, or by the fan shaft spinning, or by the whole thing rattling, or........? In other words, what kind of noise is being experienced? Different sounds have different causes and it is hard to diagnose the cause from the description: "making a lot of noise after it warms up". The suggestion about using a teflon lubricant is good, as long as you remove the fan from the computer and are very sparing with the lubricant and don't over-spray the whole fan. Be sure to stay away from WD-40. It is like cockroaches - a little bit gets into every little gap and it flows along the outside of wire insulation.