Modern life is loud. The jolting buzz of an alarm clock awakens the ears to a daily din of trucks idling, sirens blaring, televisions droning, computers pinging and phones ringing  not to mention refrigerators humming and air-conditioners thrumming. But for the 12 million Americans who suffer from severe tinnitus, the phantom tones inside their head are louder than anything else.

Often caused by prolonged or sudden exposure to loud noises, tinnitus (pronounced tin-NIGHT-us or TIN-nit-us) is becoming an increasingly common complaint, particularly among soldiers returning from combat, users of portable music players, and aging baby boomers reared on rock ’n’ roll. (Other causes include stress, some kinds of chemotherapy, head and neck trauma, sinus infections, and multiple sclerosis.)

Although there is no cure, researchers say they have never had a better understanding of the cascade of physiological and psychological mechanisms responsible for tinnitus. As a result, new treatments under investigation  some of them already on the market  show promise in helping patients manage the ringing, pinging and hissing that otherwise drives them to distraction.

The most promising therapies, experts say, are based on discoveries made in the last five years about the brain activity of people with tinnitus. With brain-scanning equipment like functional magnetic resonance imaging, researchers in the United States and Europe have independently discovered that the brain areas responsible for interpreting sound and producing fearful emotions are exceptionally active in people who complain of tinnitus.