Yeah, I don't even have a rooster. So, from now on, I'll be breaking the broody hens for their own health.
FYI, I had another hen this morning starting to show similar signs of opening up her beak and letting out a muffled sound. She has not been a broody hen, so I'm thinking maybe respirator issues as mentioned by others.
I cleaned out my deep litter bedding today, blew out all the dust, and started putting in fresh litter. I don't think my deep litter was the problem, there was no smell that I was concerned about, but I had planned on cleaning out the coop in a number of weeks anyway. Having another potential sick hen just made me decide to get rid of all the old litter and start with fresh new wood chips right now. I figure a good clean up is about all I really know what to do at this point, so everything got cleaned today.