Problem Calibrating Brightness--Help Needed

[diamondfoxxx]

I calibrated brightness on my 32 inch Sony Bravia LCD (U-series) with DVE and other test patterns which appear in discs such as the Fifth Element and Ratatouille, and it seems the correct brightness comes to about 59-60. But the thing is, during dark scenes, I see that the black background behind has no depth at all and is flickering--it switches from gray to pale gray like. When I set it it to 52, it seems okay. I want to know why this--shouldn't the calibration be the better one? Then why are the black levels worse at the particular calibrated setting?