Ken Kato has confirmed in interviews and on his LinkedIn that he created the startup sound. Stan LePard has posted the shutdown sound on his SoundCloud. Bill Wolford has confirmed to have worked on the system sounds on his website. Mike Simpson is confirmed to have written the welcome music (WELCOM98.WAV) in the production notes for the movie Stick It.
MIDI files: "Canyon Music" / "Trip Through the Grand Canyon" Composer: George Stone Produced by The Music Data Company
"Passport Please" Produced by The Music Data Company
RMI files: "J.S. Bach's Brandenburg Concerto #3" Composer: Johann Sebastian Bach Courtesy of Midisoft Corporation
"Beethoven's Fifth Symphony" "Fur Elise by Ludwig von Beethoven" Composer: Ludwig von Beethoven Courtesy of Midisoft Corporation
"Dance of the Sugar-Plum Fairy by Tchaikovsky" Composer: Peter Ilyich Tchaikovsky Courtesy of Midisoft Corporation
"Claire de Lune by Claude Debussy" Composer: Claude Debussy Courtesy of Midisoft Corporation
"In the Hall of the Mountain King by Edvard Grieg" Composer: Edvard Grieg Courtesy of Midisoft Corporation
"Mozart's Symphony No. 40 in G Minor" Composer: Wolfgang Amadeus Mozart Courtesy of Midisoft Corporation