Faint diagonal lines on LCD Tv display

I've purchased a Philips 32PF5520D 32" LCD TV, but faint diagonal lines running from top left to bottom right of screen have become noticable particularly when the screen displays similar dark colours. This occurs when viewing digital sat channels or even DVD. I expected crystal clarity under most conditions, even from an LCD.

Could it be cheap scart cables? Signal input issue of some form?

Any advice would be greatly received. Thanks