My iMac is driving me crazy, it's chirping like a cricket is stuck inside. Whenever it is chirping, I mute the system volume and it stops. This leads me to believe that it's not a hardware problem. I don't have any weird sound notification stuff going, and no new applications. It's a 2008 24" iMac, 2.8ghz, 2gb of ram - the stock configuration. Any ideas ?