I noticed my boys "nip" (put their mouthes and teeth on me) and I am trying to teach them that that isn't good. When they do it i let out a loud squeak noise. Is that right?
That usually works if the boys are young but some rats will naturally nip and think it's a fun game which is harmless but don't let it go to far. Some rats start by nipping and end up biting pretty hard. If he starts to mount your hand, or "dig" on your hand, stop him immediately.
I don't think I've had any that have went from playfully nibbling to biting hard - but my current nibblers were born here and are just 8 weeks old. I don't mind too much, a few of my 6 month boys also nibble, but it's gentle and just test nibbling. Unless it is sore I wouldn't worry but it is hard to say without seeing them ;/
Toby &Teddy always run up tp me and nip my nose or ear, but in a gental way, and everyone always tries to take my fingers when giving treats haha, they get so excited.
Another thing I always found to work was when they bite/nip make sure you don't pull your hand away. If you pull it away it will reaffirm that biting makes the hand go away.