system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is it that sometimes before you receive a text, computer speakers make some sort of static noise a few seconds before you receive the actual text?
gpt
This happens because of the way that cell phone signals are sent.

The radio channels used to communicate between the handsets and the cell tower are shared among a bunch of different handsets, so they need some way to make it so that all of them can cooperate to not get all the signals mixed up.  In some cell phone protocols, the channels are split up in time, so each handset gets a small chunk of time to transmit and then has to be silent until its turn comes around again.

In GSM, these time slices are 4.615 milliseconds long and come in groups of 8, which they transmit a little over 27 times per second.  When they transmit, they generate a little bit of current in any unshielded wires that are nearby, like speaker wire.  While the handset is transmitting, then, it's generating a current in the speaker wire a little over 27 times per second, which ends up making the speaker produce a 27Hz buzz.