Hello, this is because the solution is not stable with this solver algorithm given the constraints of the system's Eigenvalues and the user-imposed error checking setting. If you reduce the "Relative tolerance" parameter of the Simulink solver settings ("Configuration Parameters") from 1e-3 to 1e-6, for example, the results will no longer show these artifacts. The relative tolerance setting is your best option to influence accuracy control with a variable-step (Continuous time) solver, and can often be used to mitigate issues like the one exhibited with your model. I hope this helps, but let me know if you have further questions!