2. The modem's music
The brief tone. The dialing of those magical numbers. And that screech -- by God, that screech. It's musical, really, starting with a single beep and expanding into cascading harmonies of mechanical song. Then comes the satisfying bursts of static, with their climactic rush that screams out: "Sweet success, baby! We're in!"
For many of us, the sequence brings back warm memories of bulletin board systems and slow-as-molasses (but exciting as imaginable) dial-up Internet. For future generations, it'll likely be little more than an irritating noise.
See also: Modems: 60 years of hooking up