At times it drives me absolutely nuts. He's been doing it for a couple of years now - he'll invent some noise or other which he'll make in his mouth, and then gradually, over weeks, it will build and build up until he's doing it all the time, for hours on end.
He eventually stops, then a few weeks later he'll come up with a new one and the whole rigmarole starts again.
At first we just ignored it, which made no difference, as it just got worse and worse, and even his very patient teacher complained to him about it. When he does it a lot it becomes bloody infuriating!
Is this a normal habit which some children go through? He is an otherwise brilliant kid, with normal good/ bad behaviour, very close to us, etc. he is a sensitive kid, and though I would tend to assume that this type of behaviour is anxiety-related, I honestly cannot find anything which could have triggered or perpetuated it.