In keeping with the idea that the cord is acting as an antenna (ref previous suggestion about chokes) you might try coiling up the cord, perhaps around something iron, to see if the squeal changes or goes away. 

 

If the squeal changes or goes away,

    at a minimum, you're experiencing an RF induced problem and chokes have a good chance of resolving it

If not,

    your problem might still be RF in nature... but it might not!

Endif

 

Ed McCauley

IV-P (on hold)