Naz makes a sort of chattering noise with his teeth whenever he sleeps on me or if i'm not giving him scratches. I know that it's an "i like that" noise but i've also been told it can be agresshion. DO u think he might not like being scratched.
That chattering noise is called bruxing. Usually they make that sound when they are relaxed and happy. I do know that they also make that noise when they are very stressed, but im sure your rat is comfortable. My rats do that all the time when being held and kissed and loved on.
It could also be nerves I've heard. I have two rats that will brux when I hold them because they hate being out of their cage. But then if your rat seems content to sit and love on you I think it's just comforting.