Simulink scope giving out "noisy" output

So I have a simulink model that gives output of error signal fed back to a PID controller. The problem is that its very "noisy" (as can be seen below); whereas it is supposed to be flat (as shown in the 2nd picture). I can see that the shape of the noisy response is overall similar to the correct one; its just the noisy oscillations that make them different. Does anyone know why? I have chosen a stiff ode solver but this problem keeps persisting.

[Raj]

You have not attached any 2nd picture. Did you try adjusting the tolerances?

[Arvind Sathyanarayanan]

Ariel, attaching the model will help us answer the question better.

Are your reference and feedback signals noise free? Have you tried playing with your PID gains?