Normally the computer will make a sound when it is turned on. Sound is produced because there is a fan in the power supply unit (power supply unit). The fan used to cool the power supply. Noise is also produced from the fan used to cool the processor. Usually both sound will be heard as long as you install the computer.
When you install a computer, hard drive will spin. It will also produce sound but the sound is not continuous. Computers will also be out a "beep" once. These markings start with a good computer. this beep sound if prolonged or repeated, it's a sign you have suffered computer hardware and does not work well.
If you want noise can be reduced tu la install the washer on the screw that fasten the fan or hard disk in the computer casing. Just cut only. want to lose sound without doubt no. Another way, open the computer casing and clean the dust that is in the computer. Make sure there is no hair stuck in a fan. Dust and hair may interfere and remove the fan spin loud noise.
If you put the computer on the table, do not forget to put the rubber base to absorb vibration and reduce noise being diverted to the computer table.