Hi Nathan,
You can use the lsim command to get a general response of your controller. I think you want to see the response when there is noise added to the input command. The code snippet below will do this for you.
t=(0:.001:7)';% time vector
u=ones(size(t));% input vector
n=randn(size(t));% Normal distributed samples
y=lsim(mc,u+n,t);% System response to step + random noise
% Plot PID response to unit step with added noise
figure;plot(t,y);grid
Sometimes the noise is added in at a separate point in the system as a disturbance. For example, it might be a disturbance that is added after the PID controller. But you would need to re-create your system object with the second input to do this.
