Winding up clunking noise

I have a Volvo S-60 2.4T AWD. When I am driving slow, when I turn, cranking the wheel, either right or left, in drive or reverse, I hear like a winding up sound coming from the rear of the vehicle then it will slow down and then a big clunk noise will happen that shakes the car. My friend looked at it today and thought that it may be in the front wheels but after looking at it while I was cranking the wheel and moving slowly he thinks it may be something more. Do you know what it may be? Please help! How much of a job might it be? Thanks, Jake