I find it interesting that no one has considered other types of waves. It is completely possible that they communicate through radio waves produced by chemical reactions within their bodies, or possible by subtly altering the electromagnetic fields around them, assuming their planet has one. A plethora of possibilities exist, and sound may actually be primitive and brutish to any other species.
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Consecutive posts mergedThen again, they might have no form of communication but writing, assuming they can see. Mabey they had to develop writing before communication could take place, which would give them a much higher literacy rate than us, if nothing else.