Guardian's attack sound plays for anyone within render distance, while the volume doesn't diminish based on Distance.

As shown in the attached video, Guardians play their laser sound for everyone within render distance at the same volume whether they are 50 blocks away or 1.

In the video you can see a player summoning a guardian and a squid, teleporting ~30 blocks away, and still hearing the sound of the guardian's laser.

Spyglass is used to observe more clearly.

 STEPS TO REPRODUCE

1.  Use either the summon command, an ocean monument, or a spawn egg to get a guardian.

2. Leave the guardian with a squid.

3. Fly, swim, or teleport away.

You should hear the sound no matter how far you get, as long as it is within render distance / entity distance.

EDIT: I am not sure if this is a bug or not, but it keeps happening to me, and scares me every time. I am living next to an ocean monument, but the guardians are playing sounds even though I'm about 30-50 blocks away from them.