Before developing "normal" T, I experienced fleeting T as an electrical buzzing once in a few months. Since T I have basically two types of fleeting sounds: One is when everything goes silent and a tonal eeeeee happens which is high frequency, but lower than my regular T. That lasts about 1-3 minutes. The other one is the same as before, electrical buzzing, and it normally lasts for a shorter period of time.
I don't know if that's fleeting T, I guess it's not, but some mechanical stuff, but when I put foam earplugs in, my more problematic ear, the left one, starts to have thumping. But it's not constant. If I change the position of my head, it stops, but later comes back.