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The Avett Brothers showed off their harder side on NBC's "Late Night with Jimmy Fallon."  On Monday's episode, the folk-rockers put their own "gentler" twist on metal classics like Metallica's "One." 

The performances -- which also included Iron Maiden's "Run to the Hills" and Black Sabbath's "Iron Man" -- were part of a bit promoting a fake album dubbed "The Avett Brothers Sing Heavy Metal."  Fallon joked that it's the perfect record for anyone who likes the "sinister and aggressive themes" of metal but wishes the music was a bit "sunnier." 

Of course, the Avett Brothers also stuck around to play one of their own tunes.  They debuted the track "Vanity" from their upcoming album "Magpie and the Dandelion" with a little help from Soundgarden frontman Chris Cornell.  The band's new record is due out October 15th.