Sneezing/wheezing meat chickens.

Good day,
I am very new at raising meat chickens. This is my second year. I have 24 meat chickens. I noticed yesterday that some of them are sneezing and making an unusual noise. I clean the coop every two days. I also have 26 baby chicks in the same coop (which are caged separately). The coop is 8 x 12. I allow my birds to free range during the day and at night I put them away for fear of coyotes. What am I doing wrong? I did not have this problem last year.
I am also worried for my other chickens on the property. I have 37 laying hens and a few decorative chickens, 10 to be exact. I just love these animals. Excuse the pun but great chicken soup for the soul. Everyone should own a chicken or two. They are marvelous to have and very funny to watch. Even the meat chickens who are not pretty have character. If anyone can help me, please, I would really appreciate it. Thank you in advance for your help.