Originally Posted by LinearEquation
Not an extra ground, isolate the ground. Make sure the tablet and charging brick are grounded well. Is your outlet/house grounded well? Can you use an outlet with nothing else plugged into that line?
You say this only happens when fully charged and not until? I wonder if there is a problem with the battery perhaps over charging. Have you switch charging bricks? Switched cords? Does the charging brick get warm? How about the back of the tablet?
Edit: Are you using the official cord and charging brick? That can make a difference. If not what are the specks of the brick you are using?
Another new piece of information discovered today: The high-pitched whine only happens when the battery is 100% AND when the screen is on. When the screen is off, everything is fine.
So far I have tried:
1. Directly plugging into the outlet the stock Nexus 7 charging brick & cord.
2. Using the following bricks: Stock charger, Anker 40W 5-port USB charger, Amazon Kindle charger, Moto G stock charger. I've also tried all the cables that came with these devices as well as any other microUSB cables I've got lying around the house.
3. My device is not hot at all, and neither are the chargers.
Thanks a lot for your help so far! Looks like what I need to do is to turn the screen off to charge my device, and then unplug it when I want to turn the screen on & use it.