This is my first post, so I take one line to greet everyone.
I have the same issue on my phone (the black stripes are alot, it seems like a sort of painting, as someone has shown in photos). The fact that I can see is that on the stripes I have almost perfet black: in the other zones of the screen, in the dark, the screen is all but black (It seems no more that an LCD, with better performance). To make a comparison, the 820 of my girlfriend is darker, brighter and with better white and view angle too.
It is normal for an amoled screen to be not so black in dark? (should be the screen all black as it is for the black stripes?)
Greeting,
Massimo