OK...update...I received the replacement from Google and it has a similar problem as my first tablet. Oddly the sound is a bit different with this tablet compared with my original. This tablet makes a buzzing sound, much like electrical interference, that varies in intensity with the level of screen brightness (brighter the screen=less buzzing sound). The sound is also present when I touch the screen with my fingers while it is plugged into the charger. As others have reported, the sound is present but not as loud under the conditions I described, when the battery is not fully charged. The problem is most severe with the screen brightness turned down to a watchable level, a fully charged battery and the tablet connected to the charger.
I don't think that this tablet is quite as bad as my original as far as the noise issue goes, but the new tablet has a good bit more light bleed around the edges of the screen. So it seems that if I keep one of the two, I have a choice between less buzzing sounds when charging or less light bleed around the edges of the screen.
The issue with the buzzing sound is kind of trivial since the battery lasts for 6-9 hours depending on use. Although it is a bit disappointing that a $400 tablet with seemingly the best hardware available seems to suffer from some design flaws. What concerns me more is a thread in another forum about this same issue, in which a person describes this annoying hum when using an external drive connected to the tablet. I don't have a way to test my tablet while connected to an external drive...
Light bleed is such an annoying defect. Once you notice it, it becomes soo obvious. I have never owned an Apple product, but this situation has made me consider spending the extra money. Ipads seem to have similar issues. So if I were to abandon the Nexus 10, I cant find anything comparable that doesn't suffer from design/manufacturing issues.
Are my expectations too high? A $400 tablet with HD display and 6-9 hours of battery life, but I have to put up with intermittent buzzing and light bleed?
Not sure what I am going to do yet, but thanks to all who have replied to this thread.