Some of that may indicate that the noise is most likely mains bourne.
Although we have 230V, single phase power supplies to our houses the main cable runs are usually 400V,3 phase (+ Neutral). Typically in a row of houses each house is fed, in sequence, from each of the three phases** (+ Neutral) so mains noise carried on one of the phases will likely be highest at every third house.
** house 1 - phase 1; house 2 - phase 2; house 3 - phase 3; house 4 - phase 1; house 5 - phase 2; etc.
Call me 'w23'
At any given moment in the universe many things happen. Coincidence is a matter of how close these events are in space, time and relationship.
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