If Rigidbody components connected with Joints are jittering, open the Physics window (Edit > Project Settings, then select the Physics category) and try increasing the Default Solver Iterations value to between 10 and 20.
If Rigidbody components connected with Joints are not accurately responding to bounces, open the Physics window (Edit > Project Settings, then select the Physics__category) and try increasing the Default Solver Velocity Iterations__ value to between 10 and 20.