baby doesn't cry even when hungry?

Co
My baby almost never cries. The only time he has cried (and it's very rare, maybe once or twice a week) is when he is overly tired. When he is hungry he has obvious mouth cues and I feed him on demand. 
At night he does 4 hours once then 2hours thereafter. Even at night he doesn't cry he just makes some grunting noises and I feed him. Should I wait until he starts crying to see if maybe he can go longer at night?