Thanks all for your responses. General consensus is a pobblebonk frog.
Every summer our dam comes alive with Pobblebonks, Rocket frogs and a few other varieties, especially after good rain or storm.
It's kind of nice for an hour or two, but they quite often go from late afternoon to early morn! The dam is about 80 metres from the house. I'd hate to have it any closer!
The combined froggie calls are a bit reminiscent of a corroboree.