"UPDATE (31-Aug-2013) This is getting major coverage on Canada TV. Checking on Twitter, the mystery mongers are out in force saying it's apocalyptic. Here are some other suggestions I found:
"trumpets of Biblical proportions"
HAARP (not active)
Horn of Gondor (my favorite)
and regarding the last one – check out THIS video and don't tell me this doesn't happen."
Sounds like a perfect match to me!
That's it!! I agree. I've heard that sound so many times when I lived up north not far from the railroad station. Forgot all about it after moving away (30+ yrs). Very loud at night and also in different weather conditions. It sounded so familiar to me in those fake videos. Can't believe I didn't catch that. You should collect that $60,000!