Sound comes from a series of vibrations, and all the sounds you heard in the experiment occurred because of vibrations and energy. Sound travels in waves. When a source, or something that produces sound, vibrates, it produces kinetic energy. Your vocal chords and the strings on a guitar are both sources which vibrate to produce sounds.
Sound energy is in the form of waves, which travel outward in all directions from the source.
Without energy, there would be no sound. Let's take a closer look at sound waves. Waves are made up of compressions and rarefactions. Compression happens when molecules are forced, or pressed, together. Rarefaction is just the opposite, when molecules are given extra space and allowed to expand.