(no hawks around, thankfully)
Just a warning not to discount the chances of a resident hawk. I have lived in the same place for about 15 years and never seen a hawk around my house. It was not until we got some ducks that I noticed them looking to the sky and realised there was a hawk flying fairly high up. That was a few years ago, and I now realise that there has always been hawks around. I have never had any problems with my ducks or chickens (I think there is a lot of food for them in the area), but I regularly see the ducks looking to the sky and sure enough there is a hawk.
As for Currawongs, as a teenager we lived in a house that backed onto State Forrest. There were many Currawongs, and they are very smart and resourceful birds, and often seemed to be in groups. I am sure you know if they are in your area (pretty hard to miss their calls), if they are, I would be making sure either you are able to supervise or the cage is very large. I doubt noise detergents will work long term, once they realise there is no threat they will ignore them. I wouldn't suggest a feeding station (even blocks away), they seem to protect a territory, and you will only end up with a larger population which will ultimately need to move out from the station to create their own territory.
I am a big fan of the Currawong (they are a fascinating bird, used to love having them, the Kookaburra and Lorikeet come around for an afternoon feed). With that said, I remember many occasions where a Kookaburra would be sent on its way by 3 committed Currawongs, so I would certainly not trust them unsupervised with an eclectus. My fear would be less of predation, but more likely them ganging up to drive off the eclectus (who of cause will have no escape). I could see them surrounding the cage and scaring your eclectus, either causing her to injure herself as she panics and attempts to get away, or being attacked from different angles as she tries to escape the other Currawong.
Sorry to paint this type of picture, but I would hate to say nothing and have you move forward and have something go horribly wrong. If I was going to do something like this, in an area I had concerns with, I would make the cage attached to the window and have the back open (so when the window is open your eclectus can move out to the cage, but always has the option to escape back into the house). If that's not possible then it is probably best to supervise.