WHAT HAPPENS IN VEGAS STAYS IN VEGAS: To no one’s surprise, Clear Channel announced this morning that it will mount what will be the third annual iHeartRadio Music Festival. The event, set for Sept. 20-21 (the first weekend of fall), will again take place at the MGM Grand in Sin City. More than 17 million people tuned in to the 2012 iHeartRadio Music Festival, lured by a star-studded lineup that included Taylor Swift, No Doubt, Bon Jovi, Prince, Aerosmith, Jason Aldean, Lil Wayne, Swedish House Mafia, Usher, Green Day, Rihanna, P!nk, Brad Paisley, Calvin Harris, Enrique Iglesias, Mary J. Blige, Linkin Park, deadmau5 and Pitbull. Last year’s gathering generated north of 1 billion social impressions and more than 50 million text-to-win contest entries. The 2013 lineup will be revealed this summer. CC also announced its continued partnership with Macy’s, bringing back the “Macy’s iHeartRadio Rising Star” contest, which spotlights up-and-coming musicians; the grand prize is a performance slot during the fest. (3/28a)