well i'm not a doctor and this is just my personal statement....please do not take that the wrong way.... you might have anxiety and depression but the problems you experience, and i can only go after what you have stated it sounds you like you have a problem with your step dad and not the noise only. his presents is what you don't like and everything he does and every sound that comes from him irritates you.
medication can help you with anxiety but not if you like someone or not.
I think you should think about why you feel this way....you don't like him because.....?
Have a talk with him....maybe you both need to talk things out...a therapy would probably be very useful.
I hope this gave you some idea and help you face the problems you have with your step father.
I agree with ladyblue22, I think there is something about your step dad, that somehow you dont like. Although it may not be him personally that you cant stand. Is he the only male in your house, Do you still see/ talk to your dad, Have you had negative past history with a male? you have to know what it is you cant stand, is it the noice, the thought of germs, do they seems happier to you, dont worry if you dont know the answer, just think about it next time something annoys you.
I was going through the same thing for 3yrs, I took up boxing, I didnt have much money so I set up a punching bag at home. ( this is to help with the rage/fire/anger etc, feeling insde)
I took up gardening, (I too also went outside when I got pissed off). it started off just weeding around where I sat, crying. then slowly bit by bit has started to take over the backyard. If gardening is not for you try painting or model making, a puzzle, woodwork, bike making, anything that you can complete over a long time.
I found playing music with a mp3/ ipod helped aslo, (keep a watch on you mood if the song you are playing is making you feel worse you need to change it, you are trying to make your self feel better.)
I did to therpy as well which helped me figure out some of the answers questions.
Dont worry too much about the self harm, its your way of coping, (as long as your not needing first aid and you are not happy about it) Once you have sorted out the other problems it will soon stop. so dont worry. Suideal thoughts are hard.... very hard I know how you feel. some how you get through it just when you feel that way tell yourself you are working on the problem and you are strong, trust me you are stong! you put that post on here, asking for help because you really do care. Its not going to happen in a month or two it may take 1yr or 10 but it wont be the same anymore if you make changes other wise it will stay the same.
If you need any advice just ask, happy to help if i can.