99 Explorer front end noise

I just bought a 99 explorer 4 days ago. I notice that when I put it in 4 wheel and turn, the car jerks alot and makes a loud whining noise. It also squeeks. I know that it is normal for the car to jerk a little when its in 4 wheel but I have never heard the whining and squeeking before. I took it back to the dealership ( which is just a little family owned place ) and told the mechanic and he said it is normal. I understand you cant tell me with any certainty without actually driving the car yourself, but can you tell me if it sounds like there is something wrong. And if so, what it could possibly be.
Thank you