Not sound, but visual: The moment the video stream goes from blurry to crisp.

The opposite, connections that drop or slow down, the sound of music that is buffering or got automatically downgraded to the worst available quality.

There is still a lot of emblematic sounds, the skype calling sound, netflix loud bang bang, the iMessage or messenger notification pop sound, etc.

But there are all from company sound design and the same experience as the dial up sound.