Vaiśeṣika Sūtra 2.2.31

2.2.31

nityavaidharmyāt |

nitya-vaiadharmyāt—owing to difference in property from what is eternal.

27. (Sound is not something which only requires to be brought to light), because it differs in property from what is-eternal.

The difference of Sound from what is eternal, is observed. Whereas, as in “Caitra speaks,” the existence of Caitra, Maitra, etc., even though they are covered from view, may be inferred from their voice; and whereas that which reveals, e.g., the lap, etc., is never inferred by that which is revealed, e.g.. the water-pot, etc.; therefore Sound is only a product, and not something which requires to be brought to light. This is the sense.—27.