Wow! Kinda Krazy!
I have a similar "ghost" in my system, but I know what it is, from my 70's CB radio days. Every now and then, I hear "talking" coming over my system. It doesn't matter if it is on or not. If I am listening to CD's or LP's or the radio. It effects all speakers in the house and even the two in the backyard.
One of the teenage or early 20 year old kids in the neighborhood, has a amplified CB in his car and when he gets close, he comes over my speakers. Now it does not sound like Mexicali radio, it sounds like a young person on a microphone being an idiot. [8o|]
I don't know if this is your phenominon or not, but I wish you luck figuring it out.
Dennie