Default Screen twinkle

i am on emmc hummingbird cm10.1.3 stable rom, my NOOK HD screen sometimes twinkles for one time or two, it usually happens when i turn on the screen or unlock the screen. the screen would have a quick unusual light flash, then becomes normal.

very strange. is there something wrong with my device? this does not seem to happen when i am on stock rom.

did this happen to your device?