I'm sorry I don't have any experience with this, the only thing I can think of that would cause the smell is maybe he needs his anal glands expressed? Your vet can do this for you, or your groomer, and there are also some how to videos on how to do this as well. Does Chubbs drag or scoot his bum on the ground? Or does he leak any fowl smelling liquid from his bum? These are signs that the anal glands need expressing or cleaning. My guys have make this same sound it sounds like a yawn and a squeal together. Lol. Must be a Bully thing.