I have hypothyroidism and have been on Synthroid for about 30 years. I developed tinnitus a good 15 years ago. I believe mine started shortly after attending a concert. We had front row seats. One of the speakers was to the right side of the stage in close proximity to our seats. Whether or not that was the cause, I’ll never know. My right ear was affected first then soon afterward both ears. Sometimes my tinnitus seems louder than other times. I have gotten use to the constant noise which sounds like cicadas 24/7. Interesting that some meds make the tinnitus worse. I haven’t experienced this as yet.