Well, I definately think it is static, but I think it has to do with more of the insulation in the car. I think it is actually a problem with the vehicle. I had a rental car that did the same thing independent of the weather.
I live in Canada, and it is dry here, and I am not experiencing this shocking in my MP3. However, last year living in Virginia, I had a rental car, and the Ford would shock the hell out of me. I definately think it is the car and not the weather.
I would talk to your service department, about your Laser Blue "shock machine". Something is building up potential in the car's body. It might be that the car has a bad ground or poor insulation. I think it is time to put one of those strips that hang from the back of the car grounding the vehicle.
Or you could get a static strap and connect it to the car body while you are in it. This will prevent shocks as well.