Ear ringing and other abnormal ear noises is medically called tinnitus. People with tinnitus perceive buzzing, roaring, and pulsitile sounds when no actual sound is present.
Tinnitus can arise from problems in any of the four areas responsible for hearing: the outer ear, the middle ear, the inner ear, and the brain. Tinnitus is often accompanied by hearing loss.
Tinnitus most commonly occurs for unknown reasons.
Source: http://www.rxlist.com