Hello, just a comment about the tinnitus sound when you are on silence:
how many sounds do you here???, maybe because i´m a musician that i
can note every detail but i can here 3 stages of the tinnitus sound,
two high pitched sounds the most disturbing is the higer one and the
classic white noise very mild, but I noted that when you don´t take
interest on hearing the sounds are less disturbing, specially in the
night when you are trying to sleep, it´s just like when you are
sleeping with somebody that uses to snore and you concentrate on "not
hearing it", as more you want to avoid the disturbance it will get you
even more tense.

the echo sound you are hearing may be produced insight your ear too of
course and may be a point to  find the cause of your tinnitus, imagine
a sound editing software, that you can alter the pitch and the quality
of a wav file(or even add echo or reverb effect!), it´s almost the
same, our body works almost in the same way to process everything that
comes from the outside of our body, where the heck is that echo sound
creating?!, just inside your ear or in the way between your ear and
your brain (a damaged tissue or fiber for example) and is caused by
what is causing you that tinnitus.