I'm going to withdrawal the question. Further research shows that physicist don't agree on the answer. There evidently is some differences on the validity of E=mc^2 concerning the composition of sound and light.
Here's another question:
You are lost in the desert. You are out of water. You can see a spring on the horizon. You run over and touch the cool water. Your mom has told you never to drink water straight out of the ground. All you have is two clean plastic cups, and no way to make a fire to sterilize the water. How do you drink the water?