Huh, I think you might be right about the caffeine. Never thought of that before!
I've had it in one ear for almost 5 years now, got it through an acoustic shock, which was preceded by a few years of listening to loud music in headphones.
It doesn't really bother me much and actually much less so since I quit drinking coffee last year (though I never connected the two till now), stopped using headphones (I try to use speakers for almost everything), started bringing earplugs when I go to see live music, and generally avoid aggravating noisemakers (things like fans, air conditioners, buzzers), especially when I'm asleep. When I go to sleep with a fan/AC running, I usually plug my ears, really helps in the morning.
Been pretty manageable for me, though my tinnitus isn't really that severe to begin with. It hasn't actually reduced though, and has probably got worse over the last 2 years, but easier to deal with.