C.G.
Yes it is normal. He has something new to experiment with and the fact that he gets a reaction from you makes it even more fun. Just try to ignore it and I think it will become old news soon. If not, I don't think there is much you can do. My sister is in her 20's and she has grinded her teeth in her sleep since she was little. The only thing she can do is wear a gaurd, but that is not really an option for your little one at his age.