My 55618 from Märklin runs very smoothly on my short (2.1 meter) shelf track in a "curve" with 13 ‰ elevation. No cars to pull.

However, my new E71 from Fine Models seems to regulate completely differently, since it (with speaker sound off) has a distinct 70-200 Hz (?) pulsing, quite audible, running uphill on the same track.

Downhill or flat they run the same. E71 runs at its lowest speed much slower than the 55681, but even at equal slow speeds the 55618 just moves while the E71 makes its own noise. It's not a problem, more like a feature that I even quite seem to like.

Could there be said anything in general about the kind of regulators that are used for the motors on these locos? E71 has a Faulhaber motor, I know that.