Well, the blast of Antarctic air I mentioned was heading for Adelaide, has arrived. We are in the midst of a cold, wet, windy spell. A good reason to have visited my local library to read science magazines.
I was re-reading Mark Pilkington's book "Mirage Men: A Journey in Disinformation, Paranoia and UFOs" (published by Constable of London. 2010. ISBN 978-1-84529-857-9.)
I came across a section on US animal mutilations which included comments that some witnesses had seen "strange flying machines" in the area. As these objects flew over, some witnesses described hearing a "'put-put-putting' or 'ticking' sound."
The question was raised "Could they be the fabled black, silent helicopters of conspiracy lore?" (p.153.)
Black, silent helicopters have been part of the UFO scene for many years, and credited as perhaps the explanation for some UFO sightings. For example, there were suggestions that some of the 1975, US missile base intrusion reports might have been due to human flown helicopters testing the security of missile bases.
"Montana was rife with UFO activity, and reports of a mystery helicopter hovering over a missile site prompted Air Force officials to cooperate with local law enforcement in investigations of strange lights and apparent cattle mutilations..." (Bullard, T E. 2010. "The Myth and Mystery of UFOs." University Press of Kansas. p.32.)
Debate has raged as to the existence of "quiet" helicopters, and their relationship to the UFO phenomenon. Some say, "quiet" or "stealth" helicopters don't exist. Others argue they are real.
Interestingly, an article in the 14 May 2011 issue of "New Scientist" (number 2812, p.21) says they do exist.
The article is headed "Stealth helicopter's secret is out."
"They might have got their man, but US forces appear to have left behind the remains of a hitherto secret stealth helicopter after their raid on Osama bin Laden's compound in Abbottabad, Pakistan.
The troops attempted to destroy the evidence by setting fire to the downed machine, but large chunks survived. What was left suggests it was a modified Black hawk designed for stealth. The engine shroud has angles edges that may make it less visible to radar, and a disc-shaped cover over the tail rotor looks as if it should quell noise. People in the area reportedly did not hear the helicopters until they were overhead."
You can find confirmation of the existence of some previously debated information in the strangest of places!