Need some TV help from you gurus....

OK so I need some help as I am having some issues with my TV...

The picture on my 52" LCD Sharp 1080p TV just isn' what it should be. The problem is specifically with dark images. It's hard to describe, but on dark images the picture is kind of "grainy". I have adjusted the picture options (color, brightness etc.) but haven't had much luck.

I went out and got a blueray player and went direct into the TV using (2) seperate HDMI cables / inputs but still had the same problem. Does anyone have a Aquos that can comment or had a similair problem. I should also point out that they even swapped my TV out so I don't think it is a hardware problem, but maybe a setting I am failing to utilize? Any advice or help would be much appreciated. Thanks.