Possible grain issue?

[neos_peace]

Um I did do a bit of a search, it really didn't bring up anything that i was looking for.

Um its a simple question really. I know the 300 has a good bit in it, however its all the way through it as well, that and its produced that way. However I've noticed that some of my BD are weird being that in some scene's there is almost no grain. however in the very next scene there is a lot of grain then the next there is none. Is it supposed to be that way. Or is there a setting I have missed.
-50" full HD plazma
-40G PS3
-HDMI for video.

AN example of what I'm refering to=TDK when bruce is talking to alfred after capturing Scare crow and the batman want-to-be's. There are scene's that are crystal clear but the next scene there is a good bit of grain, then it's gone in the very next scene.

Also I'm assuming the grain deal is when it looks like their is a snowy type of texture on the scene, like when you come up to a channel and all you get is that snowy picture is that correct?