I know what they don't wanna tell you

Wayne knows that the world is coming to an end. Thus he has a "spaceship" to take off and leave earth.

Explanation added by: Stu618

Lil Wayne is saying that he is aware of the subliminal [secret/backwards] messages behind songs by other music artists these days & that the public however, are not aware.

Explanation added by: TruthBehindItAll