Why is my PS4 controller is vibrating? How do I make it stop?

If your PS4 controller is vibrating, it is trying to tell you that you have run into a virtual end stop for Fz or whatever you have attached to the M4 port.  

If you just want it to stop - Hit the options button on the controller.  

If you don't want to have it happen again, don't press the L1/R1 buttons on the controller (The L2/R2 triggers are what set Fz positions).

If you want to learn more about virtual stops, see spectrum ST4: controlling Fz with R2 L2