Huh - I think you're on to something there. I have a female black pastel het hypo that "squeaks" faintly when she gets stressed. She won't do it when she's just hanging in her tub, but if you pull her out and she moves around a bit she starts. At first I thought it was mild RI and took her to the vet, nada. Considered stuck shed... but it's been going on six months. I know certain lines of black pastel are more prevalent for duck billing and kinking so it looks like if I breed her I shouldn't pair her with another black pastel or cinnamon sire.