There is an adjustment you can do from the outside of the box. On each side is a threaded stud that comes out with a jam nut on it. Loosen the jam nut and take a large flat screwdriver and turn the stud in until you feel resistance. Don't tighten too much or you can cause wear on the gears, ad make steering effort harder. Another good way is to tighten until it bottoms out and then back it off a quarter turn to take the pressure off. Repeat on the other side. This should help. 

If the tie rod ends are loose, they could cause it. Only fix there is replacement. The arm on top of the spindle could be loose. Tightening them can take some slop out as well.