And the ‘n’ is now much sharper and separate – try pronouncing the two versions yourself and pay attention to the lip formations that accompany the sounds. They’re quite different.
I started hearing this among high school girls – not boys, just girls (?) – about ten years ago. Then I began hearing it in young adults and now . . .
I have not heard it from people who have a southern accent (any ideas why?); it seems to occur among speakers of what used to be called “American Broadcast English” and those with New York/New Jersey accents.