Most common cause of ringing in the ears is being exposed to loud noises for prolonged periods of time.
The ringing in the ears is also known as tinnitus and the loud sounds cause permanent damage to sound sensitive cells in our ears.
You can buy some natural ear drops that will help get rid of the tinnitus "ringing in the ears".
Exercising also seems to help get rid of ringing in the ears. I'm not sure why it does but when I have ringing in the ears I exercise and the ringing in the ears goes away.