Hi Matthew, This is hard to ID from the photo. I don't think it can be an olive whistler as they are an olive brown above from juvenile to adult. The adult male developes a grey head, but there is a sharp cutoff at the nape to olive brown. From what we can see of the face, throat and beak, my best guess would be a female golden whistler.
Hi Matthew, I have confirmed Andrews Olive Whistler sighting on advice from Mike Carter at Birdlife Australia. I had no idea, from perusing my bird guides or my own sighting on Mumbulla mountain, that the colours could be so subtle. Having had my eyes opened somewhat, I can see that Andrews photos are a good illustration of that end of the colour range; so I have put his side view and back view up in the define species slots with my own photo of a more highly coloured specimen. Having confirmed that you have at least one Olive Whistler in the vicinity, I think it's possible that one or both of your recent sightings have correct ID. (I still can't make a call from the photos.) I'll leave that up to you. ... Here is an excellent Photo and (importantly) Call resource....https://www.graemechapman.com.au/library/viewphotos.php?c=562&pg=1 ... May be you and Andrew can get a handle on the size of you local population.
Cheers,
Max.