If you guys check the Wiki article, you'll see there is a differentiation between the idea of whether or not the sound part relates to "a sound a person can hear" or a "disturbance of air." The wiki seemed to suggest the question was posed without considering this technecality, and would suggest the second interpretation is what was intended. My understanding is that the core question is, when x is not observed by anyone/anything, does x still exist.

You could ask "If there is a tree that is not observed, does the tree exist."