Mac display flickering
You may have a problem with the video chip.

Here is how to tell...
  Shutdown your machine.  Hold down the shift key.  Poweron.  Bootup will be longer.
    Wait awhile while you harddrive is being checked.
  An article on how to boot into safe mode.
    http://support.apple.com/kb/ht1455

Runs OK in safe mode...
Running in Safe mode leaves out some video drivers.  Which results in your machine not using advanced video hardware. As luck would have it, you can run the safe mode video drivers in normal mode. 

Here is how:
https://discussions.apple.com/message/16057567#16057567

Look through the above thread.  See the second page.  You don't have to read through the first page.  Just go to the part where I try a solution that works.

Using the safe mode video driver results in these limitiations:
  -- OpenGL acceleration is not supported on this mac
  -- Your mac lacks quartz extreme acceleration