Yes. Sound, like vision, itches, odors, pain* etc. all are sensenation created by the brain. Usually they result from some external stimulation but none is required. Evolution has produced this result as it normally aids survival. People do haulcine visions, have itches, and heard sound with no external stimulus. When sounds are heard with no physical cause it is: " Tinnitus is the medical term for "hearing" noises in your ears when there is no outside source of the sounds. The noises you hear can be soft or loud. They may sound like ringing, blowing, roaring, buzzing, hissing, humming, whistling, or sizzling. You may even think you are hearing air escaping, water running, the inside of a seashell, or musical notes. Tinnitus is common. Almost everyone notices a mild form of tinnitus once in a while that only lasts a few minutes. However, constant or recurring tinnitus is stressful and make it harder to focus or sleep. It is not known exactly what causes a person to "hear" sounds with no outside source of the noise. " Blue quote from: http://www.nlm.nih.gov/medlineplus/ency/article/003043.htm * Many people have "pain in a leg" but the cause is in their lower back. Some the nerves normally providing the brain with signals to process about their leg's environment and internal conditions, are being simulated to discharge by pressure against them in the spinal cord. BTW: The correct answer to the tree falling in the forest is: There is no sound, IFF there is no creature's perception of it. There is only compression and refraction waves in the air.