For a long time I have glued a small spacer to the c-hubs on my TC4 to physically limit the steering angle and it reduces the chatter to virtually nothing.
When you look at the steering at full lock on the inside wheel the way the steering arm works once you get past a certain steering angle the steering arm has almost no control over the hub and it allows the chatter, I will put up a pic tonight of the spacers on my car.