Tip: try moving further away from the computer if you can while singing (or speaking or whatever it is called in rap music..). The computers fan may make a lot of noise that will get captured if you are near (at least with some mics). Also close the windows, especialy if there is a road nearby. Oh, and i didnt mean the operating system! =D
PS: is the file called "vocal hiss" the one without noise reduction? Man, how did you get that bad noise in it? Though I dont know much I think I can say that you definetely can not get that out of it without making it sound awfull in another way. I think you really got to record it again, and before that fix the problems that cause the hissing. I dont know what is causing that but I can tell there is some major problem.
PS2: Though I dont like hiphop the mixdown sounds cool! I hope you get the problems solved. Keep it going. =)