By default, CSE HTML Validator will play a "bad" sound when there are errors or warnings and a "good" sound when a validation has no errors or warnings.
On Windows XP, the default sounds used are "C:\WINDOWS\Media\Windows XP Critical Stop.wav" for the "bad" sound and "C:\WINDOWS\Media\tada.wav" for the "good" sound.
On Windows Vista and Windows 7/8, the default sounds used are "C:\Windows\Media\Windows Critical Stop.wav" for the "bad" sound and "C:\Windows\Media\tada.wav" for the "good" sound.
NOTE: CSE HTML Validator uses sounds already installed on your system, so if these sounds are not available or installed for some reason, then you may not hear any sound. If this is the case, then you can still configure CSE HTML Validator to use sounds by telling it specifically which sounds to use.