I am on Lion and was having similar problems with coreaudiod over 100% and crippling the system. I have also read people on Snow Leopard having similar problems. Eventually I found that the /library/preferences/audio folder (that is the root /library folder, not system/library or username/library) was missing (this may even have been self inflicted, ironically, following some online advice on how to speed up my system!) Roland's solution should work, or you can as I did just copy the above audio folder from another Mac (I used my partner's who is on Snow Leopard and it worked fine). Another useful bit of info I picked up during the process is whilst you're sorting all this out, if your system has ground to an almost halt, you can disable the coreaudiod process using the following commands in terminal:
To load or unload coreaudiod temporarily:
sudo launchctl load /system/library/launchdaemons/com.apple.audio.coreaudiod.plist
sudo launchctl unload /system/library/launchdaemons/com.apple.audio.coreaudiod.plist
To load/unload and have this persist even when rebooted:
sudo launchctl unload -w /system/library/launchdaemons/com.apple.audio.coreaudiod.plist
sudo launchctl load -w /system/library/launchdaemons/com.apple.audio.coreaudiod.plist
The unload will disable all the audio but gives you your memory back whilst you replace your audio folder, then just run the load command and reboot.
Cheers