Bad sector gear, bad steering gear, bad steering bearing, bad tie rods, low tire air pressure, bent spindle or axle. Jack up the front end and see if anything changes. Remember we are not standing next to you with a beer in hand seeing what you are talking about. Try to paint us a better picture, what do you see under the unit when turning the wheel, is there excess play in the steering wheel, do the axles, spindles and wheels look straight? Did this occur suddenly or slowly has gotten worse? We need your help now.