Many gaming boxes with several fans can experience excess noise. The CPU fan may also be noisy.
There are some simple and easy steps to deal with the problem.
A thin sheet of rubber like that used with a bicycle inner tube can do wonders. Cut into small ¼ inch squares, the rubber can be wedged between the fan and the chassis. Then when the screws are snugged, the rubber acts to dampen vibration noise. This can be done with the CPU and chassis fans.
Hard disks can also have ¼ inch squares wedged into the mounts to help cut down on noise from them. The hard disk is not generally that bad compared to fans however we recall a Fujitsu 20GB IDE disk that was very loud.
Using better thermal material for the CPU can make a difference too. The CPU fan run harder if the thermal conductivity is poor.
Fan control front panel boxes are another option. We have seen models with 4 independent channels for fans. These are popular with extreme systems. Reducing fan speeds can cut noise considerably.
Having the proper air flow does help as well with CPU fan noise.
Originally a rear exhaust fan was used remove heat. Early 80mm fans were not very effective so 120mm and larger fans have taken over.
Front intake fans helped cool disk cages and they also provide the system with a source of cool air. The complements the rear fan with positive air flow.
The top exhaust fan is the most recent development that arose when the PSU was moved to the bottom of the chassis. By having a rear and top exhaust fan removes heat rapidly from the CPU and regulator.
The front to rear air flow puts a lot less stress on fan blades which reduces noise. Green energy efficient fans are available which are less noisy.