Russian Woodpecker

The Russian Woodpecker was a notorious Soviet radio signal that could be sporadically heard on the shortwave radio bands worldwide between July 1976 and December 1989. It sounded like a sharp, repetitive tapping noise, at 10 Hz, giving rise to the "Woodpecker" name. The random frequency hops disrupted legitimate broadcast, amateur radio, commercial aviation communications, utility transmissions, and resulted in thousands of complaints by many countries worldwide. Because of its extremely high power output (over 10 MW in some cases), the signal became such a nuisance that some receivers such as amateur radios and televisions actually began including 'Woodpecker Blankers' in their design.

• http://en.wikipedia.org/wiki/Russian Woodpecker