Indeed. Is the "sound" the brain's interpretation of the vibrations and pressure waves perceived by the eardrum and auditory nerves, or is the sound those vibrations and waves in and of themselves, with no further "processing" necessary for it to be called "sound"? Perhaps we need another new word involved to differentiate the one from the other in discussing "sound"?
It's did it make a sound, and revolves around the nature of what a "sound" is. The tree certainly fell.