If the Chimney Swifts in your chimney have nested (during June – August in Wisconsin), and they were successful in brooding their eggs, then you will hear some chittering/chattering/squealing noises.  (If you have a working fireplace, closing the damper will minimize the noise and will also prevent a baby swift from accidentally falling into your fireplace if it falls from the nest.) These noises are the sound the chicks make when they are awakened by the return of their parents to feed them.  Be assured – this noise is the sound of happy babies.  The noise can be somewhat loud at times, but know that it is only for the short period of time that the nestlings are unable to fly. Once the sound of the babies becomes noticeable, they are usually only fourteen days or so from fledging. Once they can fly and hunt on their own, you will no longer hear the noises.