Together with other abnormal ear noises, ear ringing is medically called tinnitus. Buzzing, roaring, and pulsitile sounds are sometimes perceived when no sound is present in persons with tinnitus.
Tinnitus can arise in any of the four sections of the ear: the outer ear, the middle ear, the inner ear, and the brain. Tinnitus is often accompanied by hearing loss. For a description of the anatomy of the ear, see MedicineNet.com's the Anatomy of Hearing and Balance article.