I had an mri done last year and had ringing in my ears the very next day. It was constant but at times I wouldn't notice it if there was other noise in the room (t.v., radio, conversation, etc). About a month later, I was placed on a prescription of methadone for chronic forefoot nerve pain. Methadone is said to be one of the few opiates that can help with that.
Well, unfortunately the pain is something I still am wrestling with but the tinnitus went away within a month. I don't know if it's gone because of the methadone but it might be worth a try. It wasn't a particularly high dose I was on, about 30mg a day. One thing you should do when taking the methadone is load up on fiber. The stuff will bind you up like nothing I've experienced before.
Hope this helps and please let us know if it does. By sharing what works, we can all live a better life. Best of health to everyone.