It's a downward tone and dragging out the end of words, ending in a sizzle, yeah. The girls who do it also tend to be a little nasal-y, too, but the reason why I don't like it is because they're forcing their voices to go to an uncomfortable spot in their throat.

It's pretty common among female 20-30somethings, regardless. I don't have it (too much theater) and most of my friends don't have it, but I know pleeeenty of people who speak that way.