In some types like terrier xs they can yip and its nothing to do with how they started ,bedy whippets and grey xs along with other types of terrier base lurchers will yip no matter how you enter them ,I have never rushed a pup and always do me best not to over run a youngster but it can happen ,I can live with the odd yip but screamers are no no ,watch Phil Lloyd's video with his old bedy lurcher it yips but still a good dog.
I think it could be excitement like been said when a juckel makes a yip now and again ,you either live with it or get shot but personally if the dog doing the job an