i just did a 3min mp3 of the strange sound, to me it sounds like
a wire that has been pulled tight and the wind blows over it.

Yeah, it almost sounds like one of those, what are they called, moosecall
thing? It's a little box or tube with a tight wire or rubber band rigged to it,
and when the wind blows over it, it gives a sound that, now that I consider it,
DOES sound a bit like this signal on 10.512. I just can't recall what they were
called, but they are supposed to scare moose away from electric fences and
other places you didn't want a moose loitering.
Moose loitering may be illegal, actually.
Linus