To clean out dust I use an air gun connected to a big air compressor (I did this just recently actually and saw that there was way more dust than I thought). Do it outside, and think about what you will wear because dust will fly everywhere (if it's as dirty as mine was). Safety goggles are a good idea.
If your computer's fans are thermally controlled, you can try
CPUIdle. It's a program that makes sure that when your processor is idling it is in the lowest power state (without affecting performance) and can be set to act more agressively if the CPU temperature rises above a certain level. The idea is that by using CPUIdle to keep your computer cool, the fans will not work as hard or as loudly.
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