Whenever my lizard is in the tub (and only when she is in the tub, so I'm not worried about an infection because it never happens any other time) she will occasionally inhale and exhale with a little hfpfhpshdfph sound. She's completely fine and often likes taking a bath (will just sit there and sometimes move around a bit--not stressed or frightened or floofing her beard). She also hasn't been doing this her whole life and has only started doing it like within the last 2 years or so, I'm not entirely sure because I hadn't ever thought much of it. Why does my precious baby go hvhvhfhfhhf?
as long as you keep an eye on the dragon while its bathing to make sure it cant drown, it's nothing to worry about.
my Agni does this after every bath too. and is also a recent behaviour. not sure what changed, he never used to do it, but it happens and you'll learn to ignore it
If she is otherwise OK I wouldn't be too worried about it. I'm not sure what's causing it. Can you take a video of her doing this? You can upload videos to a host like vimeo or youtube and then post a link to it here.