The growling sound is the sound of a baby bird begging for a
feeding and/or just enjoying the feeding he is getting. If
you are hearing that sound very often between feedings, you
may want to feed him more often and start introducing adult
foods also. Things like warm veggies, cooked pastas, cooked
brown rice and so on. Put it on a shallow saucer at first
because one way they learn to eat different things is by
playing with it more than eating.
As for keeping him on his cage, that's a lot harder. You are
now his flock and in effect, his mother and he is going to
want to be with you all the time. That's normal. The best
thing to do is to just let him be with you when you can, and
for his safety, put him inside with the cage door closed when
you can't be supervising. Good luck.