Thanks for joining the Graphics community.
In this case, you are mentioned the problem happens when the laptop is working without an external monitor? correct? The laptop works fine if you connect an external monitor, right?
Have you updated laptop BIOS?
I received the laptop a few days ago and it already has the latest Dell's Bios (A10) onboard.
I did what you asked me to do and I unplugged the power cord and I then connected the laptop to an external monitor (a 46" LCD TV Full HD Sony Bravia KDL 46W905A) using a Lindy HDMI 1.4 shielded cable.
I spotted another problem, as you can see in the attached picture: a very grainy image displayed on the external monitor; about this issue I plugged a different external display, a Samsung 22" HD Ready TV, and this one, which has a lower resolution, hadn't such a grainy image but it had artifacts and washed-out colors).
I tried to set the Intel driver but anything changed.
In this test the laptop screen had the flickering problem too but the external displays didn't suffer of it.
As I wrote, the problem is not related to my laptop but others have exactly the same issue.