Default [Q] Screen flicking/corruption - warranty advice please

I've got strange flickering issue with my phone. I've had a search around and the videos I have seen on youtube aren't the same as the issue I am having. I have tried the disable hardware overlays option but this hasn't solved it. I have uploading a video on youtube which shows 2 recordings of the issue, one after the other, each slightly different.

http://youtu.be/FYSzR9fCVU4

Can anyone advise what this might be?
The annoying thing is this has the 2nd time this has happened and its been "repaired" under warranty. What worries me is that it is out of warranty in about 1 month so if it comes back as "repaired" and the same thing happens again it will be out of warrany and presumably Samsung wont be liable to fix it again. If the same thing happens again post warranty shouldn't they be liable? Is it worth me pushing for replacement?

thanks