When I was in high school, my roommate and I would often study till midnight and then turn on radio and listen to some Australian station which would at 12 AM sharp play their national anthem. We just loved that tune.
I had never heard it ever since. Two years ago I went on YouTube to look for it. To my surprise that national anthem sounded totally different.
Over the years I had sometimes hummed and whistled that tune. So what I rememberd wasn't imagination. My memory is something I'd bet my ranch on any day. You can bet against reality if you are confident enough. And it turned out that I was right.
The melody I remembered was "Waltzing Matilda":
http://www.youtube.com/watch?v=CXasKlTsjf8&feature=related
And there's a perfect explanation for the mystery: "Waltzing Matilda" was the Australian national anthem till mid-'70s when the Aussies decided to adopt a new one which in my opinion isn't half as good as "Waltzing Matilda".
Now who's Matilda? Matilda isn't a man or a woman. It's a thing. What thing is it? It' is..., well, keep guessing.