This is one of those speech patterns that I've noticed among my students but never really considered. Then I read the term, "Vocal Fry," and suddenly a few things fall into place.
I'm fascinated by the potential for this mannerism to represent a sort of generational in-group performance. Here's the overview:
"A curious vocal pattern has crept into the speech of young adult women who speak American English: low, creaky vibrations, also called vocal fry. Pop singers, such as Britney Spears, slip vocal fry into their music as a way to reach low notes and add style. Now, a new study of young women in New York state shows that the same guttural vibration—once considered a speech disorder—has become a language fad."Learn More: 'Vocal Fry' Creeping Into U.S. Speech
Feb 23 Update: Thanks to my pal Bon for this creepy illustration of vocal fry!