Could be something in the atmosphere, magnetic lines of force produced be the world all converging in that spot, perhaps the Bermuda triangle effect, maybe the devils corner down here. Who knows. I had an old AM radio installed in one of my old stick airplanes that would take a nose dive every time I would fly over a certain at a field I used to fly at. I used to get my kicks passing over that spot all the time. So it's not an uncommon thing.