When our flock sees a hawk in the sky (especially the roosters) they make a noise that I think sounds just like them saying HAAAAAaaaaaaaaaawwwk! They really do it when they see any predator, or hear an alarming noise. It's their predator alarm call. I guess you could call it growling. I that might be what she's doing and it might sound something like gurgling, but from the way you describe the noise, it sounds more like a breathing issue to me. Growling does not really sound like milk bubbles. Bubbling has always been a problem, in the cases I've seen.
Our hens "sing" when they are happy ,as in sitting in the sun. It might sound sort of like gurgling too. Its a very soft sound.
The roosters make a similar noise to the hen song when they've found a good nest site for the hens.
When our alpha rooster is happy and he's out with the hens and they are moving, he will chatter to them. He walks along beside them, making a continual gabbling noise. It's like he's carrying on a conversation with them. When he does this, he sounds very happy and upbeat. He does it especially when we are out in the yard on nice days and they are coming to see what treats we might have for them, lol.
Young chickens (pullets and cockerels) make a different sound than the older ones do, especially at feeding time. It's a soft rrrhh rrhhh rrrhh? noise, sounding like a question. Our Silver Laced Wyandot hen does this too and she's the only one in the whole flock, other than the young ones, who does this..
Over time, you will learn the sounds your flock makes, which are normal and which are not, and what they mean.
