I thought the point of the original question is if there's nothing around, no humans, no animals, nothing with ears and no recording equipment does it make a sound. That can't be proved. Sound is caused by the receiver .
If they could speak no doubt they would tell us if the tree made a sound. But if you dont hear it, it doesnt make a sound. It's very simple, but complex at the same time.
And of course it depends on how you are defining "a sound". Is a sound just the existence of sounds waves? or is it the perception in one's brain when those waves hit your eardrums?
Trees rot and age and get disease and they fall. But..do they make a sound in an empty forest when no-one is around to hear them? Does Childbirth hurt? not if you're the one that's not giving birth. It's deep and I'm off the bed.