Night warblers

I seek assistance to identify the ‘night warblers’.

We have just returned from a 13 week trip during which we drove across to
Perth and back. During this trip I heard a bird repeat warbling exactly a
few phrases of song at most camps. The song is different at every location
but is always repeated exactly with, occasionally, an additional repeat of
the last few lines, often in a softer tone. I know I have heard these
warbles ever since I had an interest in bird calls but, perhaps because I
don’t sleep as soundly nowadays, I am now more aware of these warbles.
Initially I thought these were the calls of Magpies kept awake by the
caravan park security lights but I also heard them, just as frequently,
when camped in the bush on black nights. These warbles may be heard anytime
during the night but are most frequent about an hour before first light. I
have heard them every morning since we got back home at Yamba, NSW. The
night warbles are never heard during the day and cease just before first
light when other bird calls start. I was out wandering around at 0430 this
morning with a torch but couldn’t locate the warbler.

Intitially I was convinced the warbles were made by Magpies but they never
include the louder Magpie notes, then I was convinced they were made by
Pied Butcherbirds. However, this morning, as soon as warbles stopped a Grey
Butcherbird started to call. I think it has to be one of these species as
they are the only species with distributions that cover all those parts of
Australia in which I heard the night warbles. I didn’t hear them whilst we
were camped at Washpool NP.

I have listened to the BOCA tapes but the warbles are not included in the
recorded repertoire of these 3 species.

I know there is a simple explanation and would appreciate your thoughts.

Geoff Ryan