Sounds like he's talking.
I have two girls (5mos tomorrow) and they did and still do a wide range of vocal sounds. One of their sounds is so load as if she's screaming (high high pitch noise) and i couldn't tell whether she was upset, frustrated or wanted to be moved. I eventually figured it out that their screams were mainly one of 'excitement'.
Soon you'll be able to figure it out also, and i guess look at their eyes and facial expression and it will tell you whether it's a happy one, excitement or scared. But i guess in the meantime, enjoy it as i understand they are talking to you or a toy. Try talking back to them when he makes the noise and you'll be surprised b/c he'll coo/scream right back.