Problem with Philips LCD TV

There is a Philips 26PF8946 LCD TV set. The problem is that, from time to time, it displays vertical stripes on the right side of the screen (about 5 inches). They can appear in every mode (tv, teletext, video input). Their width does not depend on the mode (16:9, 4:3 etc.) It takes a couple of seconds until the stripes become stable. First there appear solid coloured rectangles (like in MPEG compression). Then the TV copies one row of pixels from top to bottom. Vertical stripes last for some time and can disappear automagically or you can remove them by turning the tv off and then on again. Stripes preserve their colours even after switching channels or to teletext. It takes some time until the problem appears after first use of the tv during a day.

Does anyone know what it could be? Guarantee is already void, so I don't know if I will use an authorized service.

Thanks for help.

Marcin Szewczyk