This heterodyning where one frequency beats against another frequency to produce coinciding intermediate frequencies resulting from the sum or difference of these beating frequencies occurs in many situations, including radio waves where it was 'invented' (remember superheterodyne tranny radios).
Roads made from cast concrete blocks of the same size will cause lorries to tramp over the joints which can turn to bounce same as your wagons, ships will rise and plunge cyclicly according to their length and wave swell pitch. Even clouds do it whereby a band of one cloud type will roil in position whilst other clouds skim past.
A sideways version of this is if you try to tow many trailers such as baggage trolleys, etc as the speed increases a snake occurs which gets worse until the whiplash upturns the whole train.
Back on topic...
Model rail wheel form is defined in RP25 and NMRA has good coverage of rail form also. They also cover Hi-rail for use with large flange wheels.