I had identical issues on my G2. I had to persevere with firmware flashes to get rid of root. That was simply so that I could return it under warranty. Believe me this is a hardware issue that will persevere through whatever firmware you flash. Your motherboard needs to be replaced. If you are not rooted I would return it now. If you are rooted then you need to carry on until it shows unrooted in the box at the bottom of software update screen. Good luck.
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