Boaz

The thing to rule out, rarely, is that what you are hearing is breathing rather than calling. A call starts and stops and has a shape to it; a respiratory noise is attached to every breath.

So if you hear rattling or wheezing on each breath, or see discharge at the nostrils or eyes, swelling round the face, or a bird gone quiet and off its feed, that is a vet rather than a cockerel problem. Nothing in your description points that way.

You have a male, and you have described his call exactly. The growl and then the run of crows is the male button quail pattern: a low rumbling few seconds, then a series of higher louder notes. Hens make softer chirps and calls and do not produce that combination.

So whoever sold you six hens sold you five. The growl is one of the easier ways to sex them, and it is more reliable than looking at a young bird.