It's not the power lines that cause the problems.(well...it kinda is).
It's actually the ceramic insulators(that insulate the wire from its support structure) failing that cause the problem.
Over time, those insulators ware and crack. The wire then starts to make intermittent contact with the metal supports. It's that "arcing"(if you will) that interferes with our signals.

I heard of a guy one time that was able to determine which poll insulators were bad around the flying field. With planes and radios on...(on the ground), and one guy with a "cheapie" plane in the air. He went around to the polls and banged on them with a baseball bat. When airplanes "jittered", they found the bad insulators. They called the power company, a crew came out and replaced that polls insulators... the "case" (in Cluesous (sp) terms) is "solve-ed".

Now I'm not telling everyone to break out the "Louie-ville" and go poll hunting , but it seems like a good idea if a problem is suspect.

-Mustang51