I just watched a recent episode of Wired Science and found the segment on the "Quiet Zone" fascinating. I had no idea such a place existed.
The National Radio Quiet Zone was established in 1958 by the FCC to "minimize possible harmful interference to the National Radio Astronomy Observatory (NRAO) in Green Bank, WV and the radio receiving facilities for the United States Navy in Sugar Grove, WV" (NRAO). The quiet zone covers approximately 13,000 square miles of land between Virginia and West Virginia.
Government agents drive around in (diesel) trucks looking for stray sources of radio interference. In the Wired Science episode (see below) they mentioned finding a woman using a set of wireless speakers in their home. In another case they found someone using a broken heating pad. Wow!
Follow the link to the Wired Science videos for more detailed coverage.
Wired Science Videos: The Quiet Zone
Map: Green Bank, WV
NRAO: National Radio Quiet Zone
National Radio Astronomy Observatory (NRAO)