I know this is an old thread about the first Nexus 7, but I just got my first Android tablet, the new model Nexus 7, earlier this week. I'm here because I have the same issue and was googling about it. Seriously, the right side of the screen, middle third, the back case is slightly loose so it sort of clicks when I hold the tablet with my right hand. I hear it, it's extremely annoying. I can see this issue affected lots of original Nexus 7, apparently the fix is to remove the back cover and tighten a screw. I may have to look into that, I don't think I could take a couple years of this annoying noise from the loose back cover.
@marc_lepage developer of NeverMaze (now in Google Play!)