So tell me something that I don't know already.

When the Sony Walkman made its debut in 1979, audio researchers said the same thing. When the portable CD player hit the market five years later in 1984, the warnings were issued again.

The difference? This time experts are pointing the finger to longer battery life and seemingly endless string of hits that can be played in my ears without a break.

Just Keeps Going... And Going...

There are many portable digital audio and video players on the market but clearly the Apple iPod is the market leader with 42 million units sold, 14 million just in the last quarter of 2005.

Some iPods can play up to 20 hours straight before the battery needs recharging. Most units can hold tens of thousands of MP3 songs that can be programmed to play endlessly one after another without the user ever touching a button.

No more flipping tapes. No more changing CD's. There's nothing to interrupt the music to give your ears a break and that's what doctors say your ears need.

"If it's not given that time to rest, it can result in worse hearing loss than what have otherwise occurred," says Dr. Jay Rubinstein, Director of the Virginia Merrill Blodel Hearing Research Center at the University of Washington Medical Center.

Rubinstein is a national expert on hearing loss and iPod owner. He says iPods and other digital music players are too new to be included into any conclusive study on hearing loss tied to digital music players.

"There's no evidence at this point and we won't expect there to be because typically noise induced hearing loss is a long-duration process," says Rubinstein.

How Do You Know When It's Too Loud?

But rocker Pete Townsend of The Who recently wrote in his online diary about his hearing loss, claiming its not the result of playing too loud at rock concerts, but years of playing his headphones too loud.

Headphones and earbuds don't come with warnings when the volume is at ear damaging levels. There is no requirement for manufacturers to install limiters that could restrict output to safe levels. And the federal government does not require manufacturers to provide information on the maximum output of digital music players.

So how do you know when the music pounding in your ears is at ear damaging levels? You really don't.

"People need to know the consequences of raising the volume over background noise," says Rick Neitzel, an industrial hygienist with the School of Public Heath at the University of Washington.

His job is to measure sound levels for workers to see if they exceed federal and state occupational health standards.

Just How Loud Is Seattle?

We met Neitzel underneath the Alaskan Way Viaduct -- one of the loudest places in Seattle. It just so happened that workers were operating a loud generator underneath the viaduct, which made the ambient sound levels even higher.

"It's about 96 decibels right here," says Neitzel as he takes a reading near the generator. He uses a tool called a decimeter, which measures sound levels with a small lavaliere microphone.

"If that worker had an MP3 player on right now, at his ears it might be three or four or five or six decibels more exposure," says Neitzel. "A three decibel increase essentially makes the sound twice as bad for your ears."

As an experiment, I wore a decimeter and traveled to various parts of Seattle to try and find out how loud I need to play my iPod to hear it over the background noise.

All earbud and headphones are not made the same way. Different designs and different impedances can change how loud I need to play my digital music player over background noise.

Using the earbuds that came with my new video iPod, I found that I needed to play my iPod at 50 percent to hear my music at Gasworks Park near Lake Union in Seattle.

The park is relatively quiet. The decimeter reading averaged 72 decibels, well below any unhealthful standard set by the American Speech Language Hearing Association (ASHA).

But at a busy bus stop on Second Avenue in Downtown Seattle, where people often tune out the world with their MP3 players, the decimeter averaged 82 decibels -- that's two decibels over what audio experts say is the occupational standard for an eight hour work day. I found I had to turn up my iPod volume 10 percent to overcome the background noise.

Finally, at a popular I-5 overpass used by many joggers in downtown Seattle, the decimeter averaged 92 decibels. I found had to raise the volume of my iPod at least 30 percent more than what it was at Gasworks Park.

No Way To Know For Sure

Unfortunately, the equipment needed to measure the true output of my earbuds in decibels can only be measured in a laboratory setting, and that's the problem for consumers. We really don't know how loud the music is in my ears to overcome the background noise.

If I take Neitzel's suggestion and add 6 decibels to my ambient reading, I could be listening at 98 decibels -- which is way above the 90 decibel level set by the ASHA and other experts as the minimum level where gradual hearing loss begins if exposed to the sound for hours at a time.

Regular exposure to 100 decibels for more than a minute can lead to permanent hearing loss.

The ASHA estimates MP3 players are capable of producing 110 decibels.

But you don't have to crank up the volume. You can reduce background sound hitting your ear through noise isolating earbuds made by companies like Shure and Etymotic Research.

You can also do the same with noise canceling headphones made by companies like Bose, Sony and Panasonic. They are pricey but doctors say they are worth it.

Because once your hearing starts to fade say doctors, it never comes back.