Originally Posted by urbanknight

Tinnitus is generally a neurological response to hearing loss (so we're not actually hearing a sound), which usually starts at the higher frequencies, and tinnitus has been described as the brain trying to replace those lost pitches. Although sirens have overtones at those frequencies, their fundamental pitches are much lower. I have read that it can in fact be perceived as loud enough to distract someone, and some people will even turn up their TV or radio to try and drown it out, but my personal experience is that the intensity is low enough to hear all other sounds fairly normally. As a matter of fact, the intensity seems louder when I am consciously thinking about it, but otherwise can be ignored when going about my daily business.

That's my rudimentary understanding of it. Hope that helps.