Just got my replacement "20 iMac C2D today and the fans sound really off. I recorded a short clip. It is on for the first bit then I put it to sleep, then I started it up again. Have a listen. My main concern is the "moo" noise at the end. Sounds just like my MacBook did. Also I matched the volume at about 50% with iTunes on full so if you could tell me if it is louder or quieter than yours that would be great.