Need Help to eliminate flicker/flashing

I make a 10X10x.5 box, make all 4 of the .5 edges black with the 2 10x10 faces having the default wood grain texture. So far so good eveything is as expected. The problem lies in making a copy of the original and rotating it on the x or y axis (vertical to the original) like this:

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As soon as I make the vertical one, there is noticeable flicker or flash on the one that's vertical. It doesn't seem to make any difference if I raise the one that's verticle up off of the horizontal one, there is still very noticeable flicker/flash. It is so noticeable that it makes the shirt on my avitar flash as well when I'm close to it. Is the any way to eliminate the flicker/flash?
Thanks in advance for any suggestions/solutions.

That absolutely should not happen. Are you certain yo have the current drivers for your video card? Have you played with the preferences settings for your video, and tried adjusting some of the options there? It sounds like you're configured for an option that your video card or driver does not support well.