I used an electric toothbrush for years without problems. Then after a permanent exacerbation about 5 years ago I could no longer use electric toothbrushes as it would greatly increase my tinnitus. I tried various kinds. I finally thought a Quip would work out, and it IS the quietest, but nope, it is still too much. So, I just use a manual toothbrush and have no problems.
Just because one or many people with tinnitus don't have an issue with electric toothbrushes, it is still the case that some people's tinnitus can be quite sensitive and does react. I am very careful about assigning causation to irritants unless it is very clear and repeatable. Dismissing these observations is what the first ENT I saw did when I told him about the trauma that caused my hyperacusis and tinnitus. His final diagnosis was that I was nuts, didn't have a medical problem and needed to see a counselor. What a jerk. Fortunately, another ENT I saw had experience with this and correctly diagnosed the problems.