Sounds may play at certain events in the self check interface. These events are defined in the templates/circ/selfcheck/audio_config.tt2 template. To use the default sounds, you could run the following command from your Evergreen server as the root user (assuming that /openils/ is your install prefix):

cp -r /openils/var/web/xul/server/skin/media/audio /openils/var/web/.