Touche.
Although, I have made the point before about the vibration propagating through the vessel/tree and been dissipated as heat. Again, it comes down to the definition of the word noise. Is it a noise unless it is being ransmitted through a fluid? Probably, but I hadn't thouht that far.
Also, what would a tree be doing in a vacuum? I would have to say it wouldn't be in a vacuum to fall down in the first place.
Pie