1) It turns out the MacOS notification sound had a name, and it was Sosumi. It was used from 1991 to 2020, after which it was replaced with Sonumi. There’s a funny story behind the name.
2) These sounds have a creator. It’s Jim Reekes—Apple’s sound designer, and there’s a secret that wasn’t disclosed for about 10 years after his departure from the company.
3) The Beatles are partly the authors of the MacOS startup sound.
Now for the full story. There was a company called Apple Corps, organized by the Beatles. Its logo was also an apple (of course), hence there was a legal dispute with Apple, which ended, as the joke goes, with the agreement “I don’t give loans, and the bank doesn’t sell seeds.” Apple Inc. could use its name but was not allowed to venture into the music industry and use music-related names in its products.
Accordingly, any Apple ventures into music immediately alarmed lawyers from both sides. When it came to creating system sounds, the lawyers tensed up and asked Reekes to first, not use the name “Chime,” and second, please no melodies in the sounds. As a result, operating system sounds like Frog, Funk, Glass, and Hero appeared.
Eventually, Reekes worked hard on the startup sound and created a C major chord.
Reekes assures that while creating the C major chord, he was inspired by The Beatles’ song “A Day in the Life. I don’t know why I’m laughing here.
Returning to notifications. After much deliberation and attempts to find a neutral name, Reekes proposed the playful name “Let it Beep” in the style of The Beatles’ song “Let it Be”, but his colleagues thought it would be hard to accept. When someone suggested such a name would lead to legal disputes, Reekes jokingly replied: “So sue me,” and suddenly realized that this phrase would be perfect for the sound name. Eventually, they decided to rename the sound to “Sosumi. He told his bosses it was a Japanese word having nothing to do with music.
In macOS Big Sur, the original chime was replaced with another, which was named Sonumi. The original name was retained in the first public version of the OS, but later changed to “Sonumi. The sound file itself /System/Library/Sounds/ is still named Sosumi.aiff.
Now, the OS startup sound is completely removed. It seems you can enable it in the settings.

