Help I have a radio in my tweeter

Was listening at low levels last night and heard some offputting sound coming from one speaker - kind of a light scratchy sound - put my ear to the tweeter and found a lot of static and a barely perceptible sound of voices. As I listened further it became clear that my tweeter is picking up a radio station from somewhere. I don't own a radio so it's not in my house. Something is acting like an antenna.

I have a tube preamp and when I turn it off or take it out of the system and use the pre section of my integrated SS amp in its place, the issue disappears.

So with preamp as the apparent source of the issue, one at a time I changed out all tubes for others, changed the power cord, plugged preamp it into a different circuit, changed interconnects running from pre to power - still have the problem.

Not sure of next steps - any thoughts?