this is a hardware issue that u r facing so may be the powersupply or may be any hardware device on ur computer.
unplug the cd drive and then the hard drive at a time one by one and chk if the noise is getting minimised,
u can also unplug the plug for the motherboard and chk out...
if the noise is still not geting minimised then it might be an issue with the power supply and u have to reaplce it