Look at the arm linking the wheel to the axle. Both sides should be the same angle and that angle, when new, is 22.5* down (wheel at low end).
If uneven, or level, or up, rubber in axle is shot and axle needs replacement.
Another test is to have someone walk around inside while you stand outside and watch. If wheels move up and down, likely the axle's rubber is OK, but if the only movement is the tires
flexing, the axle's rubber is likely shot.