It seems to occur when only when passing in one direction and I would say that it occurs roughly 30%-50% of the time. The power lines are roughly 50' in the air. That's a good idea to next time stop the car directly underneath them. The first time it occurred I thought "oh great, what now." It was the 2nd or 3rd occurrance when I figured it has to do with some interference with the power lines and possibly the ignition system.