Dial-up internet was the standard way to get online in the 1990s, when home computers connected through a telephone line and a modem. The sound is the audible handshake between two modems as they test the line, agree on a speed and establish a connection, which is why it mixes tones, buzzing and static. As broadband replaced dial-up, the noise became a cultural shorthand for slow internet and the early web. It now appears in memes, reaction videos and retro edits whenever a creator wants to signal the past, patience or a hilariously slow connection.