You'll have to open it up to find out where each little dB of noise is comming from. If you have a bearing going out on the power supply, that's a 45dB racket you can get rid of. If it's a loose fan, you can put a new screw/nut in it. You can upgrade to a slower/more powerful fan. There's quite a few things to do, but you'll need to open up the case either way.