With millions of iPods and other MP3 players in the hands of consumers, the portable media players have made a racket in the marketplace for years.
Now some experts warn that the devices make too much noise.
A new study from the European Union cautions that people who listen to personal music players for too long, at too high a volume setting, may do serious damage to their hearing.
The report estimates that up to 10 percent of users could start losing their hearing within five years, and most don't realize it.
"It doesn't show up. They're not aware of the fact that they're doing damage to their ears," said Denise A. Blackmore, an audiologist with Women and Children's Hospital of Buffalo.
MP3 players have become almost as common as cell phones on buses, at malls and on college campuses, and experts warn that their popularity is part of the potential problem.
Sure, young people have always liked their music loud. But MP3 players are so convenient and powerful that users spend a lot more time with them, often at ear-splitting volumes.
"They are so accessible. They are so small. You can put them in your pocket. You could never put a Walkman in your pocket," said Marcus Deveso, a Spanish teacher at St. Joseph's Collegiate Institute who is director of the guitar program and swing choir band at the school.
Audiologists are launching educational campaigns to warn users of the danger and to encourage them to lower the volume on their MP3 players.
The music coming from those small, white ear buds is part of a larger problem, experts say.
"Over the past 20 years, noise exposure for young people has tripled," said Sharon Beamer, associate director of audiology professional practices for the American Speech-Language-Hearing Association. "Our world is more noisy. There are more and more kids who use MP3 players."
The name refers to the MP3 standard used to digitally transmit music or other audio data over the Internet in extremely small, MP3 files.
The most advanced of these portably sleek gadgets can hold and replay a tremendous number of songs, podcasts, photos, movies and TV show episodes.
"If I'm not in class, I'm probably attached to my iPod," said Percy Cramer, 19, a Canisius College sophomore from Southern California who was listening to her iPod Shuffle at the library.
The increasingly inexpensive devices can do so much more than the transistor radios, portable cassette players and compact disk players of the past.
>88 million units in use
There are about 88 million units in use in this country, and sales of the devices reached nearly $6 billion last year, reported the association, which represents electronics manufacturers and retailers.
About 44 percent of U.S. households have at least one MP3 player, up from 27 percent two years ago, the Consumer Electronics Association reported. In Erie and Niagara counties, it's 30 percent of households, a Scarborough Research survey conducted this year found.
"I love it. It does everything I need it to do. And more," said Chino Ude, a Canisius senior from the Bronx who owns a Cowon MP3 player.
European scientists reported that those who listen to personal music players at a high volume for more than one hour per day each week risk permanent hearing loss after five years.
This could affect between 5 and 10 percent of people who use MP3 players and other music players, according to the report released earlier this month.
The EU report follows up on a number of studies produced in recent years that reached similar conclusions.
Hearing loss is so worrisome because it is permanent, cumulative and -- because it's painless -- hard to detect, Beamer and other audiologists said.
Exposure to intensely loud sounds over long periods of time kills the sensory cells in tiny hairs in the inner ear, said Richard Salvi, director of the University at Buffalo's Center for Hearing & Deafness.
"When we lose them, they're gone forever," Salvi said.
There are tell-tale signs that you've been listening to music at too high a volume. If you take the ear buds off and your ears feel stuffy for a bit, or if you hear ringing in your ears, you've exposed your ears to too much noise, Salvi said.
The problem is that MP3 players are used so frequently, often at a high volume and beginning at a young age.
"It's ridiculous," said Kelsey Hodkin, a freshman who was listening to Bruce Springsteen on her 8-gigabyte iPod Touch at Canisius, referring to loud listeners. "First of all, I can hear their music, and I don't want to hear their music."
When Adam Studniarek is warming up before a soccer match, the Canisius junior puts some U2 on his iPod Nano and cranks up the volume.
"I listen to it loud. Especially before games to get pumped up," said Studniarek, 20, a Poland native who listens to his iPod for about three hours each day.
Raymond H. Hull, director of the Center for Research in Communicative Sciences and Disorders at Wichita State University in Kansas, has walked around his campus with an artificial ear to test how high people have set the volume on their MP3 players.
"I've measured them up to 120" decibels, Hull said.
About 100 decibels is equivalent to the noise generated by a jackhammer or outboard motor, while 120 decibels is comparable to a thunderclap or a live rock concert, according to www.dangerousdecibels.org.
Prolonged exposure to noise at a level of 90 decibels eventually will cause hearing loss, said Michael Stratton, assistant director for the Occupational Safety and Health Administration office in Buffalo.
While European safety standards don't allow the volume settings on MP3 players to go above 100 decibels, this government doesn't have such a rule.
Some experts say MP3 players aren't any more of a threat to hearing than any other type of music player.
But other audiologists say MP3 players are a particular problem, because of their heavy use and because the ear buds direct the music right into the user's ear canal.
"With the ear buds on, it really is concentrated within the ear," Wichita State's Hull said.
They worry that they'll see a lot of cases of noise-induced hearing loss in the next few years among young people.
The world is an increasingly loud place, with more background noise and more noise pulsing from movie theaters, home theaters, car stereo systems and sporting events than in the past, audiologists said.
"It is a noisier place, and I think society has turned these iPods into a status symbol. And I think people use these things to block out noise," said Blackmore, the audiologist at Women and Children's Hospital.
There are steps that the users of MP3 players can take to limit potential hearing problems.
If you are listening to music on your headphones, make sure you can hear someone else talking to you at a normal volume level, experts said.
Researchers at Northwestern University advocate the "6 0/6 0 rule," which means MP3 players should be used at no more than 60 percent of the maximum volume and for no longer than about 60 minutes per day.
"Just giving a time out to some of your listening is quite helpful," UB's Salvi said.
The makers and sellers of MP3 players have launched their own educational campaign, "Listen to Your Buds!," in partnership with the ASHA, the speech and hearing association.
The Royal National Institute for Deaf People goes further in pushing for the addition of a prominent warning label -- comparable to cigarette warning labels -- on the packaging of MP3 players.
The industry prefers its educational campaign and the warnings already included in MP3 player instructions.
And people who own MP3 players, for the most part, say it wouldn't make a difference.
"I don't think a label on an earphone case is going to make a difference how loud they listen to it," said Lizzy Gatto, 18, a Canisius freshman from California who has 500 songs on her 8-gigabyte iPod Nano.