What works for me usually is to reload the resource pack by going into the resource pack menu. Then, move the loaded resource pack to the left side and then back to the right (loaded) and click save or whatever. When you do, it should throw up a quick loading screen which loads the resources and should fix the audio source issue. When in the resource menu any change seems to trigger it, but if you just hit save without changing it nothing happens.
Ive had this problem many times due to glitchy audio drivers. Hopefully it works for you too.
Moving a resource pack twice no longer reloads the resources, the game is now cleaver enough to realize that nothing has changed.
So I downloaded a random texture pack, every other time I move it to the right and then down to the bottom where it won't change anything in game and every other time I move it to the left. (I can never remember the F3+T, perhaps I should stick a note to my keyboard.)
Does anybody have an easy to understand instruction for making a resource pack that doesn't change anything?
Or how to find or make a copy of the Programmer Art resource pack?
That way I could just leave it at the top of the right side without having to move it to the bottom.