If this has been your cat’s behavior since he was a kitten, you don’t need to worry. We can’t really say that he’s meowing silently. He might be meowing as loud as he can, but our ears are just not capable of hearing it. Humans can hear voices up to 20 kHz, while dogs hear 45 kHz and cats rule with 64 kHz. On the other hand, if your cat was giving you a headache and suddenly stopped meowing, this could mean either of the 6 conditions I discussed above.