It's also a throwback to Apple, post lawsuit-with-Apple-the-record-company, introducing sound to Macs. "Sosumi" is an odd (in context) but clever and reverent homage.
Apparently Jim Reekes said he didn't remember how he obtained the original sound, but left the possibility open that it might (?) have been sampled from the game Crystal Quest.
Having just listened to a bunch of Mac OS system beeps on youtube, I wonder whether the Indigo sound was sampled from the SGI Indigo workstation.
