I Have Ringing In Both Ears. The Ringing Started Two

I have ringing in both ears. The ringing started two days after starting new medicine (Phentermine & Topiramate) for weight loss. I immediately stopped taking the medicine however ringing has been non stop for 3 weeks now. I went to an ENT doctor and everything appears normal. I had an MRI of brain and everything appears normal. My doctor "does not know what to say". He feels its not a result of medicine. He said it would be out of system in 2 days. Any other similar cases ? Any other ideas what is the cause ?