As a blind person, I’d appreciate getting subtle chat notifications on desktop when the chat is in the foreground. This whould be more important for me than sounds from the background. I don’t notice that someone has sent a message and have to review the message history with my screenreader by trial and error. That’s a matter of a11y, not for becoming addicted. It would make me even more relaxed compared to having to review the history for new messages randomly.
The sounds should be rather subtle, e.g., those from Adium’s Tokio Train Station soundset. Unfortunately, I cannot upload mp3 or m4a files (only mp4).