There isn't much question that something is loose and working. The hard part is to find it. You have to examine the the front suspension very closely. Look for the telltale signs of rusty powder seeping out from under bolts. If you have 2 people and can find a way to duplicate the sound without moving the truck, then just have one person keep manipulating the problem while you try to follow the noise. Look at things like the control arms, stabilizer bars. Lube the spring seats as sometimes the springs creak.
Try lubing the ball joint if they have fittings. They can do that also if they go dry.
