I'm looking for some physical intuition as to why sound waves are quantized. I know two mathematical procedures for deriving phonons in a lattice: 1) impose the canonical commutation relations on the system ad-hoc, and 2) apply the Schrodinger equation to the lattice. But neither of these gives me any sense of what could be the mechanism by which sound is quantized in the lattice. Any reference material would be greatly appreciated. I've looked around for a while on this.