It can also be a symptom of brain cancer. My aunt passed away last year after suffering from severe tinnitus for two years, and not a single doctor suggested and MRI, they all pretty much gave her magnesium supplements and drugs to treat the symptom (tinnitus) rather than actually thinking outside the box and suggesting an MRI to be sure (which is almost free in my country). Even I nearly suggested she does it very early on but thought I wouldn't know better than doctors.
Eventually, other symptoms started appearing and only then did they do an MRI, and lo and behold, a tumor was found at the base of her skull and right behind her sinus cavity, it was pressing against her auditory nerve and was the cause of all the tinnitus. The tumor was basically untreatable via surgery and it was too late for chemo.
That was my first thought when developed tinnitus, tumor or something pressing in there. In my case it was actually related to labyrinthitis, I did get an MRI and it was my first one, oh man did I get anxious inside the tube, I feel like it's good therapy for learning how to relax hehe. Anyways, Sometimes the tinnitus loudness gets worse and sometimes get's quiet, I still haven't detected what makes it change. However! recently after getting Covid It's been louder more often which tells me maybe my nervous system was affected, idk
Eventually, other symptoms started appearing and only then did they do an MRI, and lo and behold, a tumor was found at the base of her skull and right behind her sinus cavity, it was pressing against her auditory nerve and was the cause of all the tinnitus. The tumor was basically untreatable via surgery and it was too late for chemo.