It may be detecting a signal from a component that it is hooked up to. The best solution may be to turn off the monitor at night.
I'v got an activesync 2333hd tv/monitor, i have been very impressed with it so far with one exception.
I have this wall mounted in my bedroom and have found that the nice blue light at the bottom keeps turning on during the night and waking me. it seems to turn on at different times each day and night.