The bug

There are mouse click sounds in the hiss1.ogg and hiss3.ogg cat sounds.
I expected a simple hiss cat sound. I heard the sound of a mouse click in the hiss cat sounds hiss1 and hiss3.

How to reproduce

Simply type the command in Minecraft chat:

/playsound minecraft:entity.cat.hiss ambient @a ~ ~ ~ 1 1

or

/playsound minecraft:entity.cat.hiss ambient @a ~ ~ ~ 1 0

Easier to hear with pitch 0