What is Grey doing when he makes this noise?

When I go to my greys cage and talk to him or feed him he climbs from his perch to see me and he starts making a noise.It sounds like he is painting or grunting.Sounds like a baby grunting I guess.Then he bobs his head up and down and rubs his beak on my hand or finger and nibbles and then bobs his head up and down really fast.He sounds like uh uh uh uh really shorts uhs . Today I noticed he opened his beak and showed me the inside of his mouth and I caught a glimpse of something yellow.What is yellow in there mouth or throat?He also aims his private area up against the cage and poops like he is aiming near me or something.I don't know.He is three years old.I have had him since my sixteenth bday.I have not yet been able to hold him all the time because I have been scared in the pass of him biting me.My Mother told me that he could since it.So I then stuck my hand in the cage and noticed he just wanted to nibble and play.Like a dog would playing tugawar.He just wants to pull on your fingers with his beak.One time he bit me hard though.But we got over that one. Any advice would be great on what he is doing?Thanks