[gpetilli]

Since it is happening in Disabled, it is unlikely software related.

If it is always the same motor, I would start by replacing the speed controller.

An electrical short to the frame could create some very weird behavior. With the battery disconnected, try measuring with a Digital Volt Meter (DVM) set on ohms the resistance from each terminal of the PDB connector to the frame. The inspection checklist says that this should be >10kohm (probably >1Mohm).

Last, but least likely, sometimes if the PWM cables are close to noisy power cables, the coupled noise can look like a signal to the speed controller.

Are your PWMs connected directly to the roboRio or are you using a MXP board?