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.