C.G.
I also think this can be normal, but the only different thing from the other responses I wanted to add is that you want to look at his overall development. Yes, this may be just a quirky little kid thing, but if he is fine in every other aspect, I wouldn't worry. Like another mom said, if he starts regressing in speech later, does other repetitive behaviors, etc, later on, you may want to look into it more. But, it sounds like his development overall is great so I don't think you have anything to worry about with an isolated behavior.