I don't. Maybe a little bit right as I'm starting to sing, but not at all once I get going. Most other people probably don't too. There are studies that show that speech and singing happen in different parts of the brain. **Melodic Intonation Therapy** is proven method of treating stroke victims or people who have suffered a Traumatic Brain Injury and have lost the ability to speak. It involves training the patient to sing to communicate until they reach a point where they can speak with singing region of the brain. Not a big jump to infer that stuttering—however it happens—happens in the speech centre of the brain, and singing doesn't use that part, so we don't stutter while singing.