I've only played a little of Max Payne 2 and I think that it is gritty.
I think of Noir as either gritty or not... well, obviously, but it's pretty divided. So, like May Payne is pretty noir and gritty. So is SinCity or Chinatown or 12 Monkeys but whereas Citizen Kane probably isn't.
I think of the two as very similar, but Noir as more of the style of the movie and Grit as more of a theme.