As long as there has been an Iran, there has been music and poetry. But while verse has always formed an essential part of the nation's cultural personality, over the past decade, some of Iran's best and brightest musicians have been forced underground, or beyond its borders, in a journey to tell their stories.

"Every Iranian, regardless of political and religious affiliation or takes pride in Iranian poetry, so that's why traditionally it's always been allowed to exist," says Iranian rapper/poet Efran in the latest episode of MTV's "Rebel Music," the eye-opening "Iran - The Music Never Stopped." Efran has spent his life traveling back and forth between the United States and his home country. But because of the controversial nature of his lyrics, Efran hasn't visited his home since 1998.

Why can't he express himself in the land of his birth? Because, as you'll learn in "The Music Never Stopped," despite a series of democratically elected governments after years of authoritarian rule, true freedom of expression is still elusive in modern-day Iran.

Oil-rich Iran is a Middle Eastern power whose course was forever changed in 1953 when a CIA-assisted ousted democratically elected Iranian Prime Minister Mohammad Mossadegh. The intervening years have been a struggle between those advocating a strict Islamic republic where Western music and attitudes are restricted and others longing for the more open era like the one before the 1979 Islamic revolution.

Before the revolution there was a vibrant music scene in Iran, with a number of widely accepted female vocalists, according to metal singer Anahid of the band Masters of Persia (M.O.P.). "Many of the singers who'd worked in Iran and had become pop stars had no other choice but to leave the country," she says.

As a result, many Iranian musicians were forced to make their music outside of the country, including EDM artist Natch Najafi, who lives in Brooklyn and whose sound is inspired by the chaos he experienced during the bloody, nearly decade-long Iran-Iraq War (1980-1988).

After years of living in fear and and recording in secret, he says many musicians felt they had to burrow even deeper underground following the 2005 election of President Mahmoud Ahmadinejad, whose economic policies and human rights stances drew criticism from the West and, eventually, from inside Iran, as well. "After 2005 we had no other choice [but] to go underground because we wanted to play music," Najafi says.

Some hope returned following 2013 election of reform-minded president Hassan Rouhani. Once again, though, the musicians of Iran -- who need permission from the Ministry of Culture and Islamic Guidance to perform live -- were unsure of how far they could push it. And so, they retreated to the shadows once more, writing and recording hip-hop, pop, rock, EDM and metal with the always-present uncertainty about how their music would be received by authorities.

"As soon as you decide to do social-political hip-hop or death metal... forget about it," says Efran. Just ask Anahid, lead singer of the decade-old death metal band M.O.P., who left Iran four years ago because she felt she couldn't pursue her musical muse at home.

"It was rebellious. It was a very dangerous thing to do," Anahid says of her band's music, which were forced to perform in secret for invited friends in their rehearsal space. After years of being told her vocal style was wrong by music teachers, Anahid says she realized that her primal screaming helped her achieve emotional release, allowing her to shout to the universe, "I exist, too!"

"Metal lets you express the anger that's a part of society," she says. "It's the face of the world that politicians might not want people to see, but that is our reality." That message did not resonate with Iranian authorities. At one point, security forces barged into the band's studio, confiscated all their equipment and destroyed their tapes during a album recording session, accusing M.O.P. of being satanists and arresting singer Meraj, who said he was flogged more than 100 times.

It's a trap: stay and risk arrest, or flee and pursue your music knowing that you can never return, but that your voice will help people inside and outside of Iran know what the real deal is.

"I always try to paint a clear image of what it's like to be stuck between two cultures and two different countries," says Efran, who left his family behind. "The biggest sacrifice I had make doing my music was the fact that I knew if I make the music that I want I would never be able to go back to Iran."

Tune in every week for new episodes of “Rebel Music,” which premiere each Thursday on YouTube.com/MTV.