The 120v garage circuit I've been using to charge my wife's Plug-in Prius is giving me problems. My wife came to me and complained that her car hadn't charged the last couple of nights. I investigated and found the GFI had tripped. After unplugging everything on the circuit, I found that the GFI would still trip, usually within 30s or so. I figured the GFI receptacle had gone bad and bought a new one. The new one is acting the exact same way. I'm not sure how to troubleshoot this further. I don't believe I've missed any outlets on the circuit. The breaker is clearly labeled "Garage GFI" and all of the bathrooms and outdoor receptacles seem to have their own GFIs and I haven't found any outlets that are dead. The house is three years old, so the wiring is pretty new. I hate to have to call an electrician out to fix this. Any ideas?