I found myself thinking the other day, "I would give anything to hear a fart echo through the caves at occasional random," because of course, flatulence is peak comedy.
What I gave was a couple hours of my time just to learn how to put together the simplest resource pack possible.
This was inspired by a video that I can't find for the life of me, but had me in tears.
For best results, just put it in your resource pack list, and then forget about it.
Please note: if you want to confirm that this resourcepack works, open a world where you have access to commands, and type:
/playsound minecraft:ambient_cave master @s
until it triggers. There are 19 different ambient cave sounds that play at random, so it may take a few tries before you hear it.