Macbook pro 15. Intel HD Graphics 3000/ AMD Radeon HD 6490M. Screen seems 'solarized'/pixellated at startup. disappears after 30 minutes. Any idea of cause and cure?

New Machine in Mar 2011. OS version 10.6.8

All software updates installed via Automatic update.

Screen has a 'solarized' look on start up, which disappears after about 30 mins, suggesting a 'warm up' issue?

Am aware of Nvidia issues with Macbook pro but this machine has the following graphics/display on logic board.

Does anyone have a view on this matter and a way of resolving it? Still under extended warranty.

Chipset Model: AMD Radeon HD 6490M

Type: GPU

Bus: PCIe

PCIe Lane Width: x8

VRAM (Total): 256 MB

Vendor: ATI (0x1002)

Device ID: 0x6760

Revision ID: 0x0000

ROM Revision: 113-C0170H-521

gMux Version: 1.9.23

EFI Driver Version: 01.00.521

Displays:

Color LCD:

Resolution: 1680 x 1050

Pixel Depth: 32-Bit Color (ARGB8888)

Main Display: Yes

Mirror: Off

Online: Yes

Built-In: Yes

Intel HD Graphics 3000:

Chipset Model: Intel HD Graphics 3000

Type: GPU

Bus: Built-In

VRAM (Total): 384 MB

Vendor: Intel (0x8086)

Device ID: 0x0116

Revision ID: 0x0009

gMux Version: 1.9.23