Red sex link making strange whistle sounds can hear her breathing

[Catfish M]

My red sex link is 6 months old and two days ago started making strange whistle sounds.I can hear her breathing but has no other symptoms. She eats and drinks normally and runs and hunts bugs..I don't know if this is resp. infection but it sounds like something is caught in her throat. I worry for my other 7 hens.. And can't really seperate them because of my coop is all in one and need them all in there at night for protection..Can anyone give advice for this odd question? No runny nose or any other symptoms either...