Tinitus can have its roots way back to your Childhood days, Ie Teens,
I too suffer from the most aggravating constant SSSsssSsh that sounds like escaping steam or air from a split pipe, but strangely when I am around noise ie engines big whirly things and the like it goes away, but the very second the noise ends, back comes good old tinnie,
My ENT man put the initial cause down to useing 12 bores without ear cans, sadly most of my life has been alongside weapons of one sort or another, and anything that goes bang can help you on ya way.
PeterR-B