
Sadly this happened to me in january, it happened a few times and always when feeding, puppy had a rattle sound too and then his growth slowed down at about 3 weeks, as things progressed i suspected a heart defect and sadly my vet confirmed at 4 weeks old that he had a hole in his heart and i made the VERY difficult decision to pts, it broke my heart as at 4 weeks they have little characters.
i do hope this puppy is just being over greedy and it is nothing serious, just keep an eye on that little one and let us know what happens.
i wish your friend luck :)