“The startup sound was done in my home studio on a Korg Wavestation. It’s a C Major chord, played with both hands stretched out as wide as possible (with 3rd at the top, if I recall). This just sounded right to me. I wanted something really fat, heavy bass, high notes, and a sharp attack. The chiffy sound was from pan pipes and something like a stick hit (I’m testing my memory here). I wanted lots of evolving timbres, stereo phasing, and reverb for further richness.” 
“Mac people are very familiar with the sound, after restarting their machines too often. In fact, that was one of the issues I was conscious of when designing the sound. Turning the Mac on is one thing, but being forced to reboot from a crash is a totally different experience. I wanted to avoid a sound that would be associated with the crash. I wanted it to sound more like a “palette cleanser”.
“After I changed the startup sound (which required much persuasion and working around the system) the ROM engineers continued changing it with each new machine. Some of them were weak, such as the Stanley Jordon guitar strum used on the first PowerMacs. I objected to it, because that sound had no “power”. The engineer wasn’t a recording engineer, and not familiar enough with audio. The sound was hallow and without depth. When Steve Jobs returned in 1997, I heard he wanted only one sound for all Macs. He wanted the “good one” which was the one I created. At least that’s how I heard the story, and I was still working there at the time.”

 If you’re concerned that you don’t know enough about vintage Mac Startup sounds, I can recommend Mactracker, which runs on Mac or PC.