Schecklmann et al (2014) suggested that tinnitus is associated with alterations in motor cortex excitability, by pooling several studies, and reported that there are differences in intracortical inhibition, intra-cortical facilitation, and cortical silent period. We doubt that this means that motor cortex excitability causes tinnitus, but rather we suspect that these findings reflect features of brain organization that may predispose certain persons to develop tinnitus over someone else.
A large, 2014 study of almost 14,000 people found obstructive sleep apnea was linked to significantly higher rates of hearing impairment and hearing loss. Scientists think one reason for this is changes to blood flow to the ear that result in inflammation. (We know that sleep apnea causes changes to circulation and weakens blood flow to some areas of the body, including the brain.) A related factor? People with sleep apnea are at greater risk for high blood pressure, and high blood pressure can exacerbate hearing loss, according to research.
A common cause of tinnitus is inner ear hair cell damage. Tiny, delicate hairs in your inner ear move in relation to the pressure of sound waves. This triggers cells to release an electrical signal through a nerve from your ear (auditory nerve) to your brain. Your brain interprets these signals as sound. If the hairs inside your inner ear are bent or broken, they can "leak" random electrical impulses to your brain, causing tinnitus.