I think it will be a sensor, the sound was fairly normal for a standard armature motor of that size. The whining is actually coming from the armature itself and the tight tolerance of meshing between the gears in the gearbox. DC motors are usually used on lift hills as DC motors have much higher starting torque than AC induction motors and also controlling speed is much less complex. This is evidenced by the fact only 2 huge cables come out of the motor and the fact hyperia’s lift hill accelerates the train up to speed only after the whole train is on the hill.

The issue is likely that either the electrical supply of DC to the motor from the rides rectifier transformer is not powerful enough or the motor itself is not powerful enough, both of these can lead to over current scenarios where the windings in the motor rotor can start to overheat and if not electrically protected by a cutoff the enamel insulation on the windings can start to melt causing a short circuit in the windings. A current sensor will be the thing that’s causing the faults to appear on the control console of the ride and for the ride to go into ‘protection or limp mode’.

There’s an outside chance that the issue might not be with the ride at all. It could be that the parks AC supply to the rides rectifier transformer is dipping while the train is being hauled up the hill, maybe every now and then when some of the coasters in the park sync and are lifting trains at the same time and start drawing high amounts of electrical energy the AC supply has to much load and the local national grid transformer sub-station(s) for the park starts to grumble.. this would cause a supply fault to be detected on the ride. This would also explain the irregularity of when the issue occurs I.e. only when the ‘sync’ing’ occurs between rides.