I actually heard mine do the same thing for the first time today, it definetly didnt sound like a hiss, as others have stated im assuming its stress/shed related (my girl just got out of the blue phase) and i also fed her today, but had to stick my hand in the enclosure to get the water bowl out after. (first time sticking my hand in on feed day as well) so im thinking stress, does your BP have any left over shed on her face by chance?