is returning! Fox dropped a clue-stuffed promo for the show's upcoming fourth season on Wednesday, and already fans are freaking out.The trailer — which doesn't directly give away much about the upcoming competition — is all about hyping fans up for the chance to solve some new mystery identities.However, clues scattered in pictures that pop up during the brief promo give fans some tantalizing hints as to whom might be singing — or possibly what characters they might be dressed up as.The