Basically, (I believe!) it is all to do with the pickups acting as capacitors for radio signals. About 100 miles from my home in Wycombe, similar things have been reported.
Around 200 yards from people's houses was a BBC World Service transmitter station, and people's TOASTERS started to produce Russian radio! What happens is when you have 2 metal plates and a wire, they act like a capacitor. I can understand how a pickup might be affected, but a toaster with built-in radio, now that's new!!
Ben