Okay here's that gassed-about WeakAura from last night:
http://pastebin.com/m50x88k5
YOU ARE ABSOLUTELY GOING TO WANT TO CHANGE WHICH SOUND FILES IT USES because I'm a huge memelord and was using the most obnoxious ones (that make me giggle) to keep myself from getting discouraged at how bad at custom LUA I am (I'm not actually that bad, but I'm also still not fluent so there's a lot of trial and error and frustration involved).
Currently it's set to randomly play one of five audio files when Dire Beast goes on CD:
- • the Fel Reaver noise
• Auriaya's death noise
• Dis Pear
• Sindragosa's magic debuff voice line
• the Air Horn noise that comes with WeakAuras
It's not THE most intuitive weakaura to edit but it shouldn't be THAT complicated, I don't think; once you have it imported you can change the sounds you're using and how many of them you want by going to Actions -> On Show -> Expand Text Editor.

You can use the "addon" Rawr posted to find the sound paths you're looking for, or you can create and use your own—WoW can read .mp3 files and .wav files and .ogg files so whatever format your sound is in should probably be all right; the path to it starts in your WoW folder and goes from there (so if you have it just in the root folder all you'd have to put in the weakaura is the file name; if you stick it in your screenshots folder the path would be Screenshots/filename, if you put it in a folder like any other addon it would be Interface/Addons/XellAuras/filename, etc). A word on adding your own sound files: you'll want to exit and re-open WoW entirely after adding any to your wow folder so the game recognizes that they exist (just like installing a brand new addon).
That OnLoad Action is actually the only bit of the aura that's "weird," so if you wanted to you could just copy and paste that bit into any existing WA you were using, in case you wanted to... I dunno, maybe if you wanted to play a random powerup noise from Super Smash Brothers when you hit Roll the Bones or something. I've currently got it set to Action (Not) Useable: Dire Beast because I wasn't having much luck getting it to work on a combat log successful cast event (I've never been very good with that tbh lol), but back to back Wild Call procs didn't seem to break it so maybe that's all right, I dunno.
https://www.youtube.com/watch?v=RPogSnHbrUg Here's what it looks (sounds?) like in action; I've tested it on both training dummies and out in the world but not in a proper raid/dungeon environment yet. I thought about actually narrating how to set it up and change it and whatnot but then I was like man, I'm already almost guaranteed to ramble for like an hour in text, do I need to repeat myself with my actual gross voice too? :P but if that'd be helpful for someone let me know, I guess.
(I wonder if there's a way to make it less random but choose the file based on the beast summoned? That may require a proper standalone addon cos you'd have to pull the IDs of every beast summoned and I don't know if there's a way to even get that information automatically without mousing over the DB in question. That's way beyond my skills, personally—I'mma go back to painting stylized cats hiding in grass and stuff :P)
Edit: I think for now I'm going to random between some of the old Aspect noises—they're suitably beasty because they're old hunter sounds, which also gives them the benefit of a bit of nostalgia and making my hunter feel just slightly more like a hunter again:
Sound/Spells/AspectofTheBeast.ogg
Sound/Spells/AspectofTheCheeta.ogg (not actually the noise current Cheetah uses, I don't think?)
Sound/Spells/AspectofTheHawk.ogg
Sound/Spells/AspectofTheMonkey.ogg
Sound/Spells/AspectofThePack.ogg
Sound/Spells/AspectofTheSnake.ogg
Sound/Spells/AspectofTheWolf.ogg