First thing to try would be to check there is no interference from anything else. Unplug everything that is nearby, or sharing the same power adaptor - I have attached the apple support suggestions below.
Failing that, I suggest you give apple a ring if you are still under your 90 day free support or have a Protection Plan.
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Question 5: I have a monitor experiencing one of the following symptoms:
a jittering or shaking picture
discolored areas in the picture
horizontal lines cycling across the screen
distorted image
What is causing this?
Answer: These symptoms can all be caused by electromagnetic interference. All monitors are subject to electromagnetic interference. Larger monitors are affected more by this than smaller ones.
If your monitor is exhibiting any of the above symptoms, try temporarily moving it to a different location to check for interference. If the symptom does not occur after moving the monitor, then there was likely a source of interference in the area where the monitor was originally located.
Possible sources of electromagnetic interference include:
other monitors
fluorescent lights
anything with a motor (fans, air conditioners, and so on)
anything with a magnet (some mobile phones, speakers, and so on)
I have a mac mini connected to a 22" cinema display via an ADC-DVI adopter. I am noticing an annoying flickering problem after a few minutes from starting the monitor. Can anyone help?
Thanks a lot.

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