Good idea to provide winds blocks!
Do you notice if the secretions/birds have a bad/foul odor?
IF there's not really an odor, then you may be dealing with Mycoplasma. Symptoms can be treated with an antibiotic like
Tylosin bird will still remain carriers for life and you may have to manage symptoms as they arise. If there's facial or eye swelling, then that would be pus which needs to be pressed out. Care for eyes is to flush with saline, press out pus and apply an eye ointment like
Terramycin 2-3 times a day.
IF there's a bad odor, then you may be dealing with Infectious Coryza. A sulfa antibiotic is better used to treat symptoms for this disease. Since you have not lost any birds, I would suspect that Mycoplasma is more likely.
VetRx is a remedy that can be used to help alleviate minor respiratory symptoms, but it would be similar to using Vick's Vapor Rub for pneumonia. It won't necessarily hurt them, but sometimes you need further treatment.
The gurgling may be from the respiratory illness, but I would check their crops to make sure they are emptying overnight. (Should be flat before they have eaten or drank anything). See that they have a source of grit so they can process foods properly.
I would also check inside their beaks, just to make sure they don't have any lesions, yellow or white pasty material.
Here's more information about diseases
https://edis.ifas.ufl.edu/ps044