[Greg McKaskle]

Are you using Y cables for the PWM connection? Either way, I'd follow the PWM cable from the roboRIO to the motor controller pinching and jiggling it to see if you can make this happen. I've generally seen it at the Y-merge of the Y cable, and rolling in your fingers will make some motor controller see false edges and do a short (100ms) or less glitch. When tracing the cable, be careful not to be near chain or other pinch points. And I'd pull breakers on all but one circuit.

Greg McKaskle