take your door panel off, and tighten the bolts/screws inside. Mine was doing the same thing. I found out that a few bolts and screws had gone loose inside.
have you checked the felt tracks that go around your window? Per courtesy's nissans site, they extend into the door a good amount. Maybe the're bad inside the door?^ Here is my dilemma with that, mine shake like a salt shaker when they are half way down but my window rubber is perfect and they have rattled that way since I got it in 04.