First up, Majority of cases of ringing(Tinnitus)in the ear don't have any serious cause, so don't worry. Your Audiogram is within normal limits. I suggest you listen to faint music to mask the sound especially when it is quite. Take a MRI scan of Brain to settle once and for all that this is a benign problem.
Next Steps
Relax, Masking therapy
Health Tips
MRI Brain is suggested if needed.