If you think Beyonce sounded a little too perfect singing "The Star-Spangled Banner" a at President Obama's inauguration on Monday, you'd be right. Sources confirm that she lip-synced her performance.

Master Sergeant Kristin DuBois of the Marine Corp band, which backed up Beyonce on Monday, tells ABC News that the singer decided to lip-sync to a pre-recorded track.  Said DuBois, "We all know Beyonce can sing. We all know the Marine Corp Band can play. We do not know why she decided to go with the pre-recorded music at the last minute."

A hint that Beyonce did not sing live can be found on her Instagram account. On January 20, the singer posted pictures that showed her in a recording studio, holding a copy of "The Star Spangled Banner" sheet music.

Pre-recording a performance before a big event is not uncommon, as a safeguard in the event there are technical difficulties or other unforeseen circumstances.

ABC News confirms that Kelly Clarkson's performance of "My Country 'Tis of Thee" was live.