Other recordists have commented about unusual recordings of what sound like zippers. If this is a mimicked sound it would make sense in that one of the most often heard sounds in a campground at night is zippers on tents and sleeping bags. I had never recorded anything resembling this sound.
Early in May of 2013 my wife and I camped for ten days in Eastern Ohio. As it is early in the camping season most of the areas were sparsely populated with other campers. This particular night there was only one other unit within 300 yards of us and it was also a camper with no tents.
On reviewing my nights recording I found this unusual sound resembling a zipper.
Click here to listen to sound clip: Zipper 1