My Aluminium iMac just froze on me (not the first time recently, either) and required a Finder relaunch, which didn't happen. I hard restarted the machine and after about 40-50 seconds of startup I finally got to the Finder and just as I opened the first window a sci-fi spangly sounding 'Ding Dong!' kind of sound played. I've NEVER heard that before. There were no auto-start apps launching, and I've never heard it in any app I have anyway. What was it?