We found the majority of people listening at volumes between 100-105 decibels, which will damage hearing with repeated exposure.

"85 decibels is a safe level to be listening," says Murphy.

Headphones can also play a part in hearing loss. A Northwestern University professor found the ear bud-style earphones that come standard with most MP3 players boost a sound signal by as much as nine decibels. Since the ear buds are actually inserted into the ear, headphones that rest on the ear aren't as damaging.

"If they're not tightly sealed in their ears and the sound is allowed to go in, but still bleed out, they're probably better off," says Murphy.

When Murphy explained the potential danger to those we tested, most said they planned to be more cautious about volume levels.

"I think I'm going to turn it down a little bit," said Corby Goade, whose MP3 player output measured 104 dB.

Since few people have access to a decibel meter, it's important to look for physical signs that your music may be too loud. If people can can hear your music while your headphones are on, or if your ears ring after you take your headphones off, it's time to turn the volume down.

By Sarah Dallof
http://www.msnbc.msn.com/id/10580404/