Flowergirlie, are your parents perhaps not happy because you are not pursuing 'conventional' life/career paths? Like University/job/settle down with a nice man, give'em grandkids...? (at least that was the case of my parents, sometimes!!) Or there might be other underlying reasons... Like their jobs or the money situation or whatever..
Sometimes people yell at people for seemingly unimportant things when they're really angry/upset about something else...
It may be good to find that 'underlying' cause (if there's any) and maybe have a heart to heart talk? (if that's possible?)
Sometimes it might also help if you tell 'em it's making it worse, that kind of behaviour.. Or I just walk away if they don't stop yelling.. Though ideally becoming independent and moving away would probably be a better solution...