This is exactly how I caused my tinnitus.

Athletes who use iPods or wear earbuds may be at risk for permanent hearing loss.

...Northwestern University audiologist, Dean Garstecki, found the same kind of hearing loss in younger people who use iPods and earbud headphones that you would typically see in aging adults. Earbuds are placed directly in the ear and can boost the sound signal by as much as six to nine decibels. It's enough to cause hearing loss after only about an hour and 15 minutes.