9400m Nvidia screen flicker

This is a followup to a previous thread about "9400M display flicker on Snow Leopard" The previous topic was marked "Solved" and archived.

This problem is not solved.

Macbook Pro 5,1 2008 with 2.4GHz and nVidia 9400M + 9600M GT, OS X 10.6.4.

I continue to have the intermittent main display flickering exactly as described in the previous thread. This is not a back-light problem, and the flicker is a momentary blanking, about as fast a blink of the eye, of a portion of the screen and affecting the top half of the built-in display.

Additional notes:
- Apparently random, between 5 seconds and several minutes cycle.
- No symptoms occur when running Energy Saver > Better Performance, 9600M GT
- The top of the display is more affected than the bottom.
- The portion of the display affected varies.
- Sometimes occurs at the same moment the display turns on, while the system is booting.
- If using a mini-display port to VGA connector, the external monitor will loose then regain sync about once an hour, occurring less frequently than the built-in display flicker.
- If using a mini-display port to DVI connector the external display always works properly regardless of built-in display flicker.
- The built-in display flicker is independent of any external display behavior.
- These symptoms are not affected by swapping out system RAM.
- SMC reset does not fix this problem.
- Didn't waste time resetting the PRAM, it has nothing to do with the situation.
- The effect is not thermally correlated, it happens hot or cold.