Strange Sounds all over the World.

People all over the globe are reporting and recording strange, loud, unexplained sounds that seem to be coming from the sky. Recordings have been made in the U.S., Canada, the U.K., Ukraine, Poland, Sweden, Germany, Costa Rica, Chile, and more. As of January 28, there have been more than 140 documented events. Some might be hoaxes, but most are believed to be genuine, yet of unknown origin.
Explanations include:

• Electronmagnetic phenomena caused by solar storms, also responsible for aurora.
• The High Frequency Active Auroral Research Program (HAARP).
• A waterphone musical instrument.
• Military experimentation.
• UFOs (some of the reports below include UFOs).
• Warnings of the apocalypse (by whom or what?).
• Hoaxes.

From :    http://paranormal.about.com/od/earthmysteries/tp/Strange-Sounds-From-All-Over-The-World.htm