Granted that there might be DC in electrical network, but there it has never cause any amp to hum this much. I've live in this house for 10+ years. The D200 was connected via the same AC cords to the same outlets for 1+ year. I am trying to determine if there's a problem with the M250. Maybe the transformer came loose during shipping? or there's a faulty cap? It was a very loud mechanical hum that made me look outside the window for a garbage truck or motocycle.