Yeah na...

Has anyone else noticed the "yeah, na" phenomenon? I first noticed rugby league players doing it in interviews in Australia last year, and it is rife here in NZ. Kiwis are also fond of the multiple yeah, as in "do you have a 26inch tube?" "Yeah yeah yeah yeah..." I heard Steve answer a customer's enquiry with "yeah yeah na definately" the other day. I still can't work out if that's an affirmative or negative answer, but at least he was definite about it. Nath has taken it to a new level with various combinations, like "yeah yeah yeah naaaaaaaaaaaaahh" and "na na na yeah na yeah yeah yeah....... na", usually in text messages late at night. Is it funny, or annoying? Yeah but no but yeah but...