One is (the standard?) that you get from loud music and stress, which is the result of your inner ear / hair cells being damaged / misbehaving. Extreme-case: You permanently lose part of your hearing.
The second (rare?) is without impairment of hearing. To be honest you are the second person I know who shares my experience. And none of my doctors ever heard of this before. Most think I imagine this / or it's a psychological issue manifesting in your body.
I'd guess it's some kind of nerve pinching, maybe bones/muscles are involved too. Hard to say.
A few years back when I researched this I found at least one study with 10-20 individuals who reported this kind of tinnitus, but seems very rare. The result was something like "Many factors are involved in creating a tinnitus".
> Most think I imagine this / or it's a psychological issue manifesting in your body
That's a shame. The fact that it amplifies as soon as I tense my neck muscles should be testable within a lab environment.
I too thought that it was nerve pinching, and because of such, was always under the impression that it was normal. When explaining this to my wife, I just get blank stares :)