After I apply throttle and the locomotive throttles up, the pitch sound that indicates thottleing up sounds quite broken, it's not a smooth sound like it's meant to be?
That's how it sounds in reality. Modern electric locos make really that strange noises. That sound is not coming from the electric motors it's coming from the "Gleichrichter" (sorry don't know the English word for it) that transforms the electric power for the engines.
The word you are looking for is rectifier. But the the typical increasing humming sound is not from the rectifier, but from the inverter that creates the AC current for the motors. Wechselrichter The power from the line gets transformed down, trough the rectifier to a DC current and then trough the inverter back to a AC current for the motor. That way they can drive on all sorts of AC/DC/overhead/3-Rail/diesel power with the same inverter and motors. They just need a systemspecific transformer and rectifier.
Since the engine controls in Ruhr-Sieg are, quite sensibly, labeled in German but designated in English in that language's user manual and on-screen labels and instructions, a translation would be very handy. Any takers?