LOS ANGELES — While Adam Levine and Christina Aguilera may bicker on the reality talent show “The Voice,” the two singers are actually friends, according to People.com. Levine would even defend Aguilera against her critics who should “grow up,” he said. Aguilera, 31, has been getting flak for gaining weight. “The one thing about the culture right now, celebrity culture particularly, is people feel like they can just say nasty things about other people whether it's Christina or whether it's me,” he says. “She gets a lot and it pisses me off. Of course I have her back and of course I defend her,” he told the celebrity website. — SG