Is the noise on pavement or off?
One thing to check is the actual rolling diameter of your tires. I've had enough variations in same size tires to cause binding. Put a mark on each and make 10 revolutions across a parking lot to see how much variation there is. Put the largest and smallest together on one axle and the middle two on the other to help minimize the difference between the axles.
Binding on a hard surface when turning, even hard dirt, is normal as the front axle has to travel further that the rear.