The truth, the iMac isnt as quiet as they make out when doing processor intensive stuff like using iTunes and another program at the same time. You can turn down the settings by going to the Energy Saver under Systems Preferences to change Processor Performace under the option tab to Automatic. This should help make the fans run a little quieter, but will also slow down your computer just a bit. Now, there has been a problem with bad fans in the iMacs, so if it is making these sounds from when you first turn the Mac on and it should be hot enough to warrent fans yet, then that needs to be taken care of by Apple. Call them up on their tech support line.