PC getting very loud.

Can someone help with my latest problem? 2 days ago when i started up the PC was unusually loud as if something was vibrating inside. Then it started to make these reving noises, like a car reving it's engine. The up and down reving got more intense as I clicked on progams but everything was working fine. I restarted and got the same result. When I restared the next day no loud noises, but today it happened again. The load noise stoped 2 minutes after windows loaded. thanks! Dell xpst600p3 100 mg bus 252 cache 128ram 32mg tnt diamond viper