The falling of a tree emits sound waves that can travel through substances thus making a sound.
1. If sound is defined as the emission of sound waves, yes.
2. If sound is defined as an auditory experience, no.
If a tree falls and no one ever observes it or anything caused by its falling, then the universe in which the tree falls and the universe in which the tree does not fall are identical from our perspective.
So we can rephrase the question as, "Does anything exist until we observe it?" The answer, of course, is yes: Our observing of some event X does not make it exist; the event would have existed without our observing it. However, for the sake of practicality, if we don't observe event X, we continue our lives as if it never existed, since we don't have enough evidence to support that event X will affect us. Therefore, the answer is, "Yes, but the utility of this knowledge is 0."