[Bloody Sam Roberts]

One possible explanation if it IS electro-magnetic related;

Earth has a magnetic field. A big one. Magnetic lines of flux enter and exit the planet's crust at many points on the surface. Their house may just reside on one such point.

[Perdogg]

I was thinking along those lines.

[Oztrich Boy]

Earth has a magnetic field. A big one. Magnetic lines of flux enter and exit the planet's crust at many points on the surface. Their house may just reside on one such point.

Magnetic lines of flux only enter and exit the planet's crust at the points of weakness where lines of longitude and latitude intersect.