The dial up modem sound.
You remember it; late night, summer of '97, you just got your "Free AOL Trial" disc in the mail. Hells yeah! Version 2.5 just came out, time to get online and chat with the other six people you know with the internet. Type in your info then connect and voila! your ears are orgasmed by the dial up modem sound. But, whatever happened to that sound once the future took over and DSL, cable and T1 lan lines came in to play? Well, absolutely nothing, duh.
Except this cool dubstep rendition by Chrispy and a place on the pop culture archive shelves.
Chrispy - Dial Up (Dubstep)
BONUS: An absolute gem here! Dial up modem sound slowed down 700%, makes for creepy scary movie background music.