It's not really a noise per se, so the whole concept of "loudness" is pretty bizarre. Usually people just mean minimum masking level, but that has a lot more to do with how good your hearing is, than anything else. (Meaning that if you have two people who both have "20 db" tinnitus, but one of them has a perfect 0 db hearing threshold and the other one has 40 db of hearing loss, the first person will match at 20 db and the other person will match at 60 db, even though the "volume" is the same). Moral of the story for me is "protect the hearing you've got left and don't fret about the rest".