He is 7 and for a few years now has been making this funny noise in his mouth when he is concentrating on something - playstation/nintendo/writing etc. It is very annoying (esp to DH) but we just can't get him to stop. He really doesn't know he is doing it. We say "no noises please" and he says "ok" and then does it again in seconds.
I mentioned it to his year 1 teacher and she said to leave it and he would stop but it is still going on.
Any suggestions please?