My 4 month old?

kitten cant miow, we found him in the street a few months back, he is adorable and very well behaved only when his brothers miow for food, all that he can muster is a little tiny squeek, he is healthy and has a little fat belly so im sure he is not sick, any ideas anyone? oh and we did try to find his owner but nobody replied to any adverts or never reported him missing to any local vets.