I've run into this problem twice now on a new 17" G5 iMac and a 20" G5 iMac. The game sounds are high pitched like Mickey Mouse on helium. Eventually the problem resolved itself on the 17" iMac - not sure how. But the 20" iMac still sounds like an insane mouse on crack when running Quake3! I just finished installing all the OSX updates but no luck. It has 512MB of RAM but is otherwise stock (1.8GHz G5, FX5200, 160GB HD). Any other G5 iMac owners with Quake3 run into this problem?