I don't know where the sound/noise came from? I wasn't expecting it, and it happened so fast. It didn't feel like a backfire...like I said before, it was one loud POP..like a firecracker being lit! And then the car lost all engine/electrical power. From memory, I would lean towards the sound coming from exhaust though.
I will have to check some things over as mentioned, when I have time, and report back.