I do recall ages ago seeing an LG that had loads of grain in the shop, to the point of it looking like a very stony picture.
I thought they were all like that and it almost stopped me buying one, but i checked a few other stores and they were fine (as is my one at home, which was the same model).
If it is really really bad, then it might be worth asking LG to send an engineer.
If however it is subtle, then it might just be the film grain as others have said. This is a good thing as it's what is intended.
Perhaps worth taking your film to a store and asking to view it on other sets