http://www.youtube.com/watch?v=4PoQQ...e_gdata_player

Its the noise that you hear at 22 seconds... It doesnt sound like a croak, like the males mating call. Its not an "eh!" its a "brd-d-d-d". Sounds more rumbling, like an old engine trying to start. Is this a call of females, or males? What does it mean? is it purely territorial?