Can someone with brightness fluctuations take a video of it occuring? My PN59D7000 exhibits some black level fluctuation that is a function of the APL of the frame. I can perceive it in letterbox bars, but it's not distracting -- the entire frame is certainly not fluctuating in brightness.
For those with the issue, I assume you're in the movie preset with all eco options / motion lighting / dyn contrast, etc. options are off. Does it occur with GAME mode turned on? That disables some extraneous video processing.
Edit to add... could also try max'ing out the cell light (i.e., no more room for the display to "pop" the brightness).