Flexing my google sk33lz:
[NOTE THAT ALL FOLDERS AND FILES ARE CASE SENSITIVE!]
Step 1: File Structure
Go to your World of Warcraft/Data folder, check for a folder named "Sound" if no folder exists make one.
Now go inside the Sound folder you created (or if one already existed) now you are going to make another folder inside Sound named "Creature" (If for any reason one already existed leave it) go into your Creature folder.
Now the last folder you will make will be "WaterElemental"
Your folder structure should now look like this: World of Warcraft/Data/Sound/Creature/WaterElemental
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Step 2: Creating the File
This part is extremely simple, open up notepad, go to file/save as, save the file with the name "WaterElementalLoop.wav", save it where ever you like (also you must put the .wav after the name).
Now just move your new wave file into your WaterElemental folder, enjoy!
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All hail the mighty google.
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"There is an art to flying, or rather a knack. The knack lies in learning how to throw yourself at the ground and miss. Clearly, it is this second part, the missing, that provides the difficulties." - Hitchhiker's Guide to the Galaxy