LCD HDTV Question

In dark scenes/parts of movies and tv shows on my LCD TV screen, there are lines of darkness slightly darker than the shadow or intended darkness. They make squares on the screen. I was wondering if this is normal or if the unit has been damaged? These squares do not show when there is color or light present, only in the parts that should be purely dark.
I should ammend that these lines appear regardless of the source (digital cable, dvd player, video game system, etc.)

Just curious, what model LCD TV do you own? It sounds like digital artifacts to me. Dark scenes seem to be very difficult for digital TVs to display. Some handle it better than others.

It's a lower end Toshiba.

Ah yes, this was my original assumption but I wanted to be sure before the warranty ran out. Thank you very much.