Just keeping it short, I'm not too happy with the current notification sound.
I browsed some CC-0 licenced sounds, maybe you like some and can add them:

• https://freesound.org/people/qubodup/sounds/782969/
• https://freesound.org/people/yfjesse/sounds/235911/
• https://freesound.org/people/AnthonyRox/sounds/740423/