I am posting this here instead of under iBook support (the machine is an iBook) because the issue only occurs under OS X; booting into OS 9 does not present the same issue.
Nothing in OS X Panther can produce a sound. And yes, I have checked the mute button and volume levels.
I called AppleCare and they said to do a reinstall of Panther, which I did, with no affect. I have repaired permissions, tried under several different/new user accounts, and even done and fsck -y in single user mode.
If anybody has any suggestions, they would be greatly appreciated.