Just noticed a whistling sound

Trying to feed my adult female bp (who hasn’t eaten in like 4 months, no change to weight or appearance though), and she was hissing at me and being all huffy as I tried to entice her with the mouse, and I noticed that at the end of a hiss she makes a whistling sound. No bubbling at the mouth or gaping that I’ve seen, but is this normal? It’s only when she was hissing at me just now towards the tail end of each hiss.

Also, any tips for getting a pesky bp to eat? I’m thinking of switching from large rats to f/t quail, maybe the scent of that will do it.

An adult female big enough to eat large rats can and will go off food for months. Just wait her out. I'd start offering a small rat every two weeks if she isn't losing weight.

The whistle at the end of the hiss may be because she's starting to pop a shed, or because she's just exhaling really hard at the end to encourage the rodent to be elsewhere.