I wouldn't worry. My son did the same thing for a few weeks at this very age. I spoke with a good friend about it, who is a speech pathologist and she assured me it's VERY common and not to be concerned. She would only send him for an evaluation if this was happening around 5 or 6 years of age. She encouraged me to give him my full attention when he was talking and not to say anything about the stuttering, so he wouldn't be self-conscious. It's like their brains are moving faster than they can articulate the words.
Interestingly enough, this all happened during the few weeks prior to the birth of my second child. After the baby was born it completely stopped! I honestly think the stuttering was related to his anxieties about the new baby. Something to think about.
You already got some good advice. I wouldn't worry...totally normal.