I had it for several months and it turned out to be a symptom of high blood pressure. Once I started taking medicine for my blood pressure the ringing in my ears went away. It might be worth a health check just to see if it can be sorted.
I'm surprised that a white noise machine is recommended. Does the decibel level matter? Does it eventually make the ringing go away permanently or is it more about being able to cope with the tinnitus by drowning it out?