A mysterious humming noise in Costa Rica was caught on multiple videos during the evening of 9/01/2012. Officials blame the noise fireworks, leaving locals unconvinced.

Read More:

http://www.costaricanewssite.com/strange-sound-heard-throughout-costa-rica

http://youtu.be/HUCAVA-PYhw (Video, introduction in Spanish)

http://youtu.be/pco_g5gwZj8 (longer video, 10minutes)