I guess I must be part of the 40% of veterans, then. But why does it seem to be worse some times? In my case, I only notice it when it's quiet and that's a rare thing anyway; much too rare. Also, sometimes, like when I'm trying to go to sleep and it is quiet, some noises will sound very, very loud even when they're not, as if they're interrupting the normal ringing, which I admit sounds strange as described. Other normal sounds, even fairly loud ones, like a motorcycle going down the street, don't seem to produce this reaction.
On the other hand, I am surrounded by a lot of things that seem to be making a humming noise under ordinary conditions, like this computer in front of me.
Here's another hearing oddity: ever have a gun fired unexpectedly and have the sound amount to nothing more than a "pop?"