The Magpie wait's until you pass it's tree and before swooping it flaps it's wings loud enough to hear. Just go to the street in the intersection ahead since those streets don't have any tree's and you'll be fine.
Walking besides a tree on Parsons Street, Sunshine headed towards Sunshine Station. About 10 metres past the tree a heard a loud "SNAP" beside my right ear, turn around and I see a magpie arching back up to the tree I had just passed. No return swoop.