ORIGINAL: Lnewqban
2) Check the geometry of the front wheel.
The point of contact with the ground should be in line with the axis of steering, only better if it is slightly behind.
Any off-center will give some leverage to the obstacles to try to turn the wheel.
To do this: center the rudder and then push the airplane on a flat surface like a garage floor. It should roll straight. If not, adjust the wheel control clevis on the rudder steering arm. And, as noted, set it at the least movement possible.