Apple User Help

What app/notification is causing this sound on my MacBook Pro Late 2011

My MacBook Pro running macOS 10.13.6 sporadically makes the following sound. I’d really like to know where this is coming from. Sometimes it looks like the computer makes the sound when the Ethernet cable and/or the power cable are disconnected, but I haven’t been able to reliably link the sound to any of these events […]