Thanks Steve, so the plug itself is acting like a mini antenna ... I can easily check the resistance from end to end and measure some other plugs lying around.
Yes, there was no SAG - engine was making normal power.

Jeff,

I have gotten RF interference from resistor type spark plugs including BR10EIX when the internal resistor element fails and an arc occurs internally.  This can be verified by checking the resistance between the center electrode tip and the end where the spark plug wire attaches.  The resistance should be in the neighborhood of 5000 ohms with a good plug and infinite or open circuit on one that has failed.

My experience is that this type of failure is unrelated to SAG.

Steve Boese