I free range as well, and lots of parasites are found in the soil. So when chickens free-range they also do get into contact with soil as well as with eachother. Theres a really large possibility that they will get worms sometime or another...
Chickens can act legthargic for lots of things. For example, when they have lots of worms infested in them...
EDIT: I dont know if it would cause the odd noise though...
IT will actually kill chickens. I do it twice a year. Its definitely important, as it can cause them to have an...