Sure. “Sound” is the internal accusative of “to hear,” just as “taste” is the internal accusative of “to taste.” That is, what we hear are sounds, and what we taste are tastes, and so on.
So if a tree falls in a forest, what is heard is the sound it makes. And if no one is there, then it makes a sound even if it is not heard.
Clearly, if you hear something, then what you hear is a sound. But it does not follow from that, nor is it true, that if it is not heard, it is not a sound. To draw that inference would be to commit the fallacy of denying the antecedent, as it is called. It would be like arguing that if Paris is in Germany, then Paris in in Europe, so, therefore, if Paris is not in Germany, then Paris is not in Europe. Clearly, Paris need not be in Germany (as it is not) but may still be in Europe, as it is. If all the people in the world turned deaf this instant, there would still be sounds that no one could hear. Why should something happening to the the ears and auditory system, make any difference to what occurs in the world?