If your device do come with a default sound for some events such as "External Power Connected", please do NOT set the sound for this event. Otherwise, two sounds will be overlapped.
You can configure each Event with a notification sound, with its own volume level. If you want to set the volume globally, please turn ON "Use Same Volume" function.
Please set a short notification sound for any event, and it should not be too long (no longer than 2 sec). Most importantly, it should not repeat itself. If you do set a long sound, you can press "Stop Sound" button to stop the playback.
Make sure you do set the notification sound and it is not set to NONE. Otherwise, there will be no sound for the event.