Loud fans are usually caused by dust if there is dust built up on the fan it can throw it out of balance and make it rattle. Just because you fan got loud doesn't mean you machine has any other problems than the fan.I would start by cleaning out the computer with compressed air. Clean off the fan blades and blow out the power supply and the heat sink for the cpu. Once this is done check your temps in the bios to see if your cooling good enough. then decide if you have other problem . A good cleaning often solves a lot of problems. Hope this helps