As soon as I ruled out the actual FiOS box shorting out I immediately assumed it had to be that outdoor outlet. I've never used that, and if I need to power something out in the driveway, I could just run one of those long extension cords from inside the garage. I'd be fine if they just disconnected it from the GFCI and power entirely...
I'm assuming the builder is going to come in and essentially just swap it for a new one which may have the same issue. We'll see.