Well one thing that can quiet down case fans and power supply's is removing the metal grills that are in front of them, ...sometimes that is what is causing the most noise and air turbulence.
I always use tin-snips and/or a dremel to remove as much of the "hole punched" guards as I can and then any that show or I'm afraid need guards I replace with the wire style fan guards like this.
http://www.svcompucycle.com/svcompucycle/58556.html