Loud noise in 4HI.......

Hi
I seem to have a problem with my 4x4.....thought u could tell me if it´s a big problem or nothing at all :)......the thing is when im in 4HI and turn the steering wheel at either right or left there is an loud noise coming from the front, almost like "dunk,dunk,dunk,dunk" and the steering isnt going smooth......does anybody here know what could be the problem....

Greatful for all the help i can get

/Sam

Are you on dry pavement when this happens, if not sounds like the front diff, of course someone would have to hear this on site to really help.