Not sure where this belongs, but it regards a friend of mine.

Whenever my friend is concentrating on something, he makes this noise. Sort of like a hum noise, I don't know how to explain it, but he only does it for a second, but he does it a lot, like, he does the noise for a second but he does it a few times.
He has ADHD.

But I'm not sure if this is something he does when he's concentrating, he doesn't know he's doing it either, though I've tried to point it out to him but he says 'what noise?' but he usually does it when he's concentrating.

I only just told him this yesterday, and he told me to point it out to him when he does it again, so I'll keep doing that, and see if he realizes he's doing it, because I'm not very good at explaining things lol.

But, yeah...
Any ideas what it could be?
He hasn't got tourettes either.

We all have little things that we do unconsciously, just sounds like it's a habit that he has.

Yeah, it really doesnt sound likemuch of anything but a habit.... I bite my fingernails when in deep concentration, run my hands through my hair when im nervous in social settings, actuallly tap my nails on the table when im impatient, yeah THATS annoying.

lol, okay, thank you, was just curious as to what it is.

I can totally relate with the finger nail biting, I do that almost all the time, sometimes without even noticing. Same with chewing my gums.

Thank you both x

yep! i chew the inside of my lip, one of many habits of mine.

it's annoying ain't it?
one minute youre just, doing your own thing, then next you realize youre chewing your gums/lip.
lol.
its weird!

I bite my nails and chew my lip when I am in deep consentration.