When Settings > Notifications > Sounds are enabled, a sound will play whenever a new message or conversation is received.
Audio will only play when the user
or agent engages with the document by clicking somewhere in the admin
area or on the page displaying the chat widget.
This is because of a security
feature of the browsers.
If the sound is set to repeat,
it will loop as long as the admin area or the chat widget page is not
open or minimized.
If the the admin area or the chat
widget page is open and visible, you will not hear the sound.