The family Cinclosomatidae contains 9 species of passerine bird, including the 3 whipbirds, 2 wedgebills, and the quail-thrushes. All are native to Australia or nearby areas.
The gronking song often ends with some "growling" sounds which in at least some cases are mimicry of possums (nocturnal marsupials), followed by mimicry of Grey Shrike Thrush (Colluricincla harmonica, Pachycephalidae).
In 8, there are three Shrike-thrush calls but no possum; again Shrike-thrush but no possum in 9; at Toonumbar the birds use Eastern Whip-bird (Psophodes olivaceous, Cinclosomatidae) instead of thrush but I've given you just the gronking.
In the example from Tamborine (11), the gronks are followed by one definite possum sound, then an unrecognised (at least by me) growl and finally three Shrike-thrush calls.