The heavy metal band Anthrax shocked fans recently by showing their softer side. The group known for thrashing guitar licks unplugged their amps and played an acoustic version of the Pink Floyd classic Comfortably Numb during an appearance on SiriusXM's Opie Radio. And the results were amazing.

Check out some more unconventional but surprisingly awesome covers. 

1. Kurt Cobain's Grunge Hymn

Before Nirvana achieved superstardom, lead singer Kurt Cobain and bassist Krist Novoselic worked on a number of side projects, including a 1989 recording session with fellow grunge rockers Screaming Trees. The session included Cobain singing a raw cover of the spiritual folk song He Never Said a Mumblin' Word

2. Sid Vicious Croons

On the surface, you probably couldn't find two iconic musicians who are more different than crooner Frank Sinatra and punk rocker Sid Vicious. But the Sex Pistols bassist proved they shared a similar outlook on life when he covered a snarling rendition of Ol' Blue Eyes' 1968 hit My Way, which was released on the soundtrack for Sex Pistols' 1980 mockumentary The Great Rock 'n' Roll Swindle.

3. David Byrne Raps

The Talking Heads frontman surprised fans at a charity event in 2014 when he put aside his New Wave repertoire and busted out a cover of Just a Friend, the 1989 hit by comic rapper Biz Markie. Byrne's rap isn't flawless -- he stumbles over the words a few times -- but his enthusiasm for the performance more than makes up for those shortcomings.

4. Jimi Hendrix's Protest Anthem

Jimi Hendrix's cover of "The Star Spangled Banner" has arguably become the unofficial anthem of the 60s. Hendrix famously used distorted guitar licks to imitate machine gun fire, bomb blasts and other sounds of war that Americans witnessed nightly televised reports on the Vietnam War. Although accepted as a rock classic nowadays, Hendrix's cover was controversial in its day. In fact, Andy Cush of Spin likens the protest song to San Francisco 49ers quarterback Colin Kaepernick's recent decision to stage a protest by sitting out the national anthem.

5. Johnny Cash's Western Grunge

In his final years, Johnny Cash put his final stamp on pop culture with the American recordings, a series of albums featuring the country legend doing covers of by covering songs by bands ranging from Nine Inch Nails (Hurt) to Depeche Mode (Personal Jesus). It's hard to pick the best track from the collection, but one that stands out is Soundgarden's Rusty Cage, a frenetic grunge hit that Cash transformed into a brooding western tune.

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