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Hearing loss began early for Josh Musto, triggered at first by a heavy metal concert and worsened by years of playing guitar in two bands. Listening to loud music constantly through ear buds may be to blame for a ringing in his ears.

“I’ve been a musician forever,” said Musto, now 21 and a junior at the New School in New York City. “There’s a lot of noise in my life.”

Josh Musto, a music student at New York City's New School, is an intern at SiriusXM radio. Mayra Ramales

Musto is not alone. Doctors warn that a steady onslaught of loud noise, particularly through ear buds, is damaging the hearing of a generation wired for sound — although they may not realize it for years.

Earlier this year the World Health Organization warned that 1.1 billion young people are at risk of hearing loss because of personal audio devices, such as smartphones, and damaging levels of sound at entertainment venues like electronic dance music festivals, where noise levels can top 120 decibels for hours.

"Probably the largest cause [of hearing damage] is millennials using iPods and [smartphones],” says Dr. Sreekant Cherukuri, an ear, nose, and throat specialist from Munster, Indiana.

Hearing loss among today's teens is about 30 percent higher than in the 1980s and 1990s, Cherukuri estimates.

“You (once) had a Walkman with two AA batteries and headphone thongs that went over your ears,” he told NBC News. “At high volume, the sound was so distorted and the battery life was poor. Nowadays, we have smart phones that are extremely complex computers with high-level fidelity.”

Cherukuri tells young patients to stop wearing headphones — especially earbuds, which place the sound closer to the ear drum, enhancing volume by as much as 9 decibels.

“It's very easy to achieve unknowingly," he said.

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According to the National Institutes of Health, repeated exposure to sound over 85 decibels can cause hearing loss. Permanent damage can happen in minutes, experts say, and when the damage is done, it’s irreversible.

“Noise exposure in kids is a growing concern,” said Nicole Raia, a clinical audiologist at University Hospital in Newark, New Jersey.

Raia said she sees more tinnitus in young people, an early sign of hearing loss, but, “we don’t catch them until they are in their 20s and 30s.”

And because audio-screening protocols are not that sophisticated, many children with subtle damage pass hearing tests, she added.

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A study published in 2014 revealed that nerve synapses can be more vulnerable to damage than hair cells in the inner ear. When young animals were exposed to loud noise, even just once, they had accelerated hearing loss later in life.

“Within minutes of exposure, the points between the hair cells and the neurons were injured and the loss was permanent,” said co-author Sharon Kujawa, director of the department of audiology at Massachusetts Eye and Ear Infirmary.

The problem is when there is exposure to excessive noise, it goes away within a few hours.

This “hidden” hearing loss is not picked up by standard threshold tests on which all national standards are based.

Experts say the best way to protect young ears is to apply the "60/60" rule: Keep the volume on the MP3 player under 60 percent and only listen for a maximum of 60 minutes a day.

When using headphones in a noisy place like a school bus or subway, the tendency is the turn the volume up, so use headphones that cover up outside noise.

And to protect your kids, use Apple’s parental control setting to set lower sound levels on iPhones and iPods, locked in place with a password.

For small children at loud sporting events, music concerts or riding on the subway, buy ear protection.

As for Musto, he said he “got a lot smarter.”

After seeing a doctor, he only uses over-the-ear headphones and protects his ears from loud noise with customized ear plugs. He gave up earbuds a long time ago.

Today, he continues to play in two bands and interns at Sirius XM radio, doing interviews and some DJing.

“If I couldn’t hear, I wouldn’t be able to do this,” he said.