RE: If a tree falls in the forest and no one is there to hear it, would there be a sound?

Yes that is true, but basically we have the same biology, so we have very simmilar perception of most physical things. Imagine how differently would things be percieved by aliens with different anatomy - maybe something that we percieve as pleasant music would sound horrible to them, etc.
But I like your point of view, because yes perception of literally anything is very different to everyone in the sense that we have various associations with given object, such as tree. It is like Elvis's guitar - basically it is just a guitar, right? You could create exact replica, that would sound the same, look the same. But it would not be the guitar, but a guitar. :D