[Monochron]

Verify that it can happen while the robot is disabled and when the PWMs are unplugged. If this is the case then you have an electrical issues which you should be able to find by tracing each of your wires.

If you can't find it visually you could first unplug everything, then slowly plug things back in (after turning the robot off again) and finding which individual thing is causing, or part of the problem. Do this as a last resort though, as forcing your robot to short like this isn't the best solution.