I would like to know if the flickering issue happens while you are using only the laptop, without the external monitor?
Have you tried another monitor? Does the behavior persist?
Have you updated the Laptop BIOS?
You can also try our latest graphics driver provide at the following link Intel® Download Center, however bear in mind that we provided generic drivers; and sometimes these cannot be installed on other systems or the installation of them could overwrite their customizations and possibly change the functionality of the graphics.
I don't have another monitor to test my computer with. Since I can't figure out how to cause the problem, I haven't been able to test my laptop alone either. All updated versions of BIOS for my computer have nothing to do with graphical systems. I'll spend some time with only my laptop and see if anything happens.