Play Cave Sounds only when non-passive mobs spawn or despawn in a cave.

Currently, cave sounds (ambient sound effects) are hints to players that a cave is nearby. With 1.18, chunks with caves are a lot more common, so these hints aren't as important as they used to be. Pick a random location and dig straight down, and you have decent odds you'll drop into a cave (stone or deepslate) before hitting bedrock. But these cave sounds could serve another purpose.

Whenever a neutral or hostile mob spawns or despawns below y=64 where sky isn't visible, there could be a chance for an ambient SFX to play. So, you get basically the same thing as we have now (because mobs can't spawn inside solid ground), but the sounds convey more concrete information to players. When you hear a cave sound, the game would be telling that your threat environment has changed in some way: either you now have an extra mob somewhere, or there's one less to worry about.

The same thing happens in the movies: spooky faraway sound effects suggest to the audience and characters that they're not alone down here, that there's unknown dangers they might face if they keep moving forward.

If there are no valid mob spawn areas anywhere within simulation radius, you're not going to hear a single cave sound. This might be unusual unless zero mob spawns is exactly the thing you want.

Finally, the cave sound volume could be loud if a mob event happens nearby, or very faint if the mob event happens at the edge of simulation radius. If many mobs spawn at once, the SFX could sustain longer.