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Opera singer Renee Fleming will sing "The Star-Spangled Banner" live on Sunday night. Larry Busacca/Getty Images hide caption

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The current record holder for loudest crowd in history are the fans of the Seattle Seahawks, who cheered so loud that they induced a mini-earthquake. But that level of noise can permanently damage fans' hearing. Scott Eklund/AP hide caption

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Sean Morey, then with the Arizona Cardinals, celebrates after blocking a punt against the Seattle Seahawks in 2007. Morey, who suffers from post-concussion syndrome, retired from the NFL in 2010 on the advice of doctors. Stephen Dunn/Getty Images hide caption

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