Barn owls produce a variety of vocalizations, although the ‘meaning’ of them is not always clear. For example, you may hear the female ‘rasping’ repeatedly, particularly before she produces and starts incubating eggs, but we do not know what, if anything, is being communicated. BNOWs also hiss and bill-snap when threatened. They do not “hoot”. Search Youtube for examples of BNOW sounds.