Does it only happen when there's no other noise? Those are high-pitched frequencies that are always there and are too high for the human to hear, except for a slight ringing in their ears. Everyone gets it when it's very quiet. It could also be something else, though, in which I strongly recommend going to see a doctor.
Many such as you and I struggle with tinnitus. The ringing is caused by damage to our hearing from constant exposure to loud noises. While there are currently no effective cures, there are some therapies that help. Contact a qualified audiologist to have your hearing tested, and see if any of the current help available will work for you. Good luck.