An undiagnosable screen fault (flickering/glitching) I have been experiencing an intermittent screen flickering/glitching. The problem occurs where I use, or leave the laptop on for several hours, until I let the laptop rest (i.e. shut it down and leave it off) for several days, then promptly starts again with a couple of hours of use.

The flickering/glitching affects the whole screen. I don't think the attached image does the problem much justice. The whole image on screen appears to shake, moving up and down, ghosting between two 'screens'. The problem started with faint horizontal lines across the screen and then escalated within a matter of hours.

I have taken the Macbook Pro into an Authorised Apple Service Provider who were unable to diagnose the fault with their diagnostic systems; as a result they weren't prepared to replace any hardware. The service provider has proved fruitless. Has anyone else had a similar experience?
If possible, try using a second display (through Mini-DisplayPort or Thunderbolt). 

The objective is to find if the issue is the LCD panel (Screen) or the GPU (Video Chip/"Card"). 

If the issue persists on a secondary/external display, the issue is the GPU. If the issue is limited to the built in display, you've narrowed down the source of the issue to your LCD. 

Have you noticed any other patterns, such as use of Safari or other apps? Some apps, upon opening, switch from basic "integrated" graphics, to the more powerful "discrete" graphics chip, and its possible that this change is causing the distortion.

EDIT: I should also note that service providers' diagnostics are unable to detect connection issues with the LCD panel (unless completely disconnected), so any tests they run will be inconclusive if its the LCD. LCD issues simply require visual inspection, and your photo should be sufficient proof. Source: Apple Employee/tech for 8+ years