No no no, 'nawlins' is something that people from the city tell to outsiders for fun. It's a myth, like chupacabras, cow tipping, and the female orgasm.
In actuallity, all residents of the town very clearly pronounce it 'New Orleans' with a crisp northern accent when in private. "New Or-lee-annes." Also, they pronounce the famous festival 'Mardy Grass'.