I had exactly the same problem, with exactly the same equipment. I sent one back and had a new one delivered few weeks back. The new one has the same problem. Bought a new HD Cable, made no difference. It looks like interference in the dark images right? Grain like you said. Have you spoke to the people you purchased it off or had any advice from anyone else?
Hi there I just bought a new Panasonic TC-P50GT50 from best buy and for some reason the picture quality isn't as good as the TV it replaced which was the LG 50PK250 plasma from 2010. I haven't changed anything else but the TV. I'm still using my PS3 as the blu ray player and some blu rays such as Avatar show a perfect image where as others like the watchmen, Iron man, Hulk, etc. show grain in the picture, where the LG didn't. I'm not sure that there's something wrong with the TV, but I'm finding it difficult to believe that one of the best Plasma's of 2012 cant stand up up to a $699 plasma from 2010. Any help would be appreciated.