It could be a few things. If you can get access to the area where the sounds are and still be able to retreat quickly, (In case it's a momma something with babies, she might attack), you should try to visually inspect the barn loft. You may have racoons, opossum, rats, or owls up there. If it is too dangerous to get up there, than try the flour method or see if you can borrow a game camera from someone and point it at the presumed entrance/exit.
BTW, I alwso do not kill or trap wildlife. My pens are strong, and my property is frequented by Bobcat, Skunk, Racoon and Opossum. Good poultry management does not automatically require that you kill every wild animal you see. There are other methods that work just as well. Electric is a good option for those on a budget, for instance.