Tinnitus
What I can suggest is consult a good ENT specialist and you may like to check for teporomamdibular joint syndrome with the help of an orthodontist, or it could be due to stress. Since MRI scan has ruled out any other problem with the ear such as cyst or growth the best is to consult an Orthodontist through an ENT specialist. Go to a doctor who doesn't fleece you with a unnecessary tests.
Rule out any old head injury or whiplash to the neck and head while driving a two wheeler or four wheeler.
Regards,
Mathew more