Why is my XBOX 360 Slim so Loud!!!??!?

Why is my supposedly whisper quiet XBOX 360 slim so loud when playing games from the disk. When I download them to the hard drive its fine. My tech savvy dad says its because its spinning at a faster than normal rate. Its been going on for a little less then a year and working fine. I complained to Microsoft and they said that not being whisper quiet isn't grounds for replacement. I want to know what is really going on and whether or not i should complain again and keep being a nuisance to Microsoft so they will replace it. Its a black 250gb xbox 360 slim in a well ventilated area. It also recently made a loud noise when erasing a game demo from the hard drive. i suspect that to be the hard drive itself but im no technical engineer. yet. Please help, thank you.