I think you're referring to glottal stops. I get them mostly with the /i sound You can learn more about it as it relates to stuttering here: https://youtu.be/cT61_TVFed8?feature=shared Also this video, although does not relate to stuttering, it does share a useful way of stopping glottal stops from happening: https://youtu.be/GSzlXjA2SYk?feature=shared