sys-setup: Disabling UI sound effects doesn't work

[apjanke]

There's code in there to turn off the UI sound effects, but it doesn't seem to work. The check mark will disappear sometimes, but the sound effects (e.g. for file deletion from Finder or emptying Trash) still happen.

Logging out or resetting doesn't seem to work regularly. I think it eventually took effect on some boxes I ran this on, but not everywhere.