Typical thing to reduce noise is to put in filtering, generally the power companies have LC filters across the phases, and also have harmonic traps in series with the phases, typically tuned to the third harmonic so that the current is more likely to approach a sine wave. The distribution transformers though tend also to be part of the filtering, simply because they are also inductors in the path, though some utilities also deliberately include a bypass capacitor across primary and secondary of the transformers ( tuned to resonate at a predetermined frequency) to pass through the power line control signalling used to control things like power switching, line taps and street lighting, without having to run any extra communications cabling.