For some reason, when I plug in my iPhone (3G) it acts as though I am constantly plugging and unplugging it (vibrates and goes from displaying a charging and normal screen). I've tried a different outlet with the same results. Also, I have plugged my iPad in to the same cord and outlet and it charges normally. Since I mostly charge my phone at night, the vibrating is disruptive, and I'm not sure how to turn it off, if I can. What should I do?