My laptop began making unusual noises and I noticed one of the fans was running slow.
Easy! Just took it apart, cleaned everything out and put in the fan.
When you need to dust out your laptop, don't put a vacuum cleaner hose right up to the exhaust port so that it causes the fans to spin. This can shorten the lifespan of them by causing them to spin beyond their rated rpm. Just use a brush and some compressed air. If you vacuum, do it carefully.