Metchosin: I am personally sure it is "a wandering foot or a heart at rest" not only because the parallel structure demands it but also that is the way it is recorded in no less an authority than the Hootenanny Songbook.
A term I have loved for years is the old term "gabble ratchet," the cry of the wild geese as they cry. It comes from the "gabble" which is not onomatopoetic as it sounds, but is a corruption of "Gabriel." The "ratchet" is from the old word for a hound, and appears in a number of the old ballads. So the crying of the geese overhead is the baying of "Gabriel's hounds." I wonder if the term "gabble" to describe the noise comes from there rather than simple imitation. The idea of the Hounds of Heaven seems to fit right in with Alba's story.