I think it's a software issue. I noticed it too, but it was when I was using the tablet in iffy light conditions.
The problem lies in the auto-brightness. It seems that the sensor or the software or whatever controls it isn't doing it right, and it flickers. I turned off auto-brightness and downloaded a brightness toggle widget to make it easier to control the brightness, and it hasn't flickered since. I tried to recreate all the scenarios where it was most likely to flicker and it didn't do it once.
Of course, it could just be a fluke that the flicker existed to begin with, or, conversely, a fluke that disabling auto-brightness fixed it. So basically, YMMV.
Give it a go.
I also did the screw-tightening thing and I'm very pleased with how it addressed the issue. Not perfect, but I did that and the brightness adjustment over an hour ago and no issues to report.