RF picked up from cable

I just upgraded my preamp (from Superphon Revelation II to VTL 2.5) and was picking up annoying RF interference--a radio station I don't recognize--on phono stage only, loud enough to be really irritating. I wondered whether this might be entering from a couple of long RCA interconnects that I use to connect with a second system in my basement study. Disconnecting the unshielded 40-foot Radio Shack interconnects I am currently using (while looking for something better but still cheap) from tape out to my downstairs integrated amp did nothing; but disconnecting the shielded cables that carry the downstairs output back to Aux in stopped the noise. Weird! Any suggestions on how to kill the noise while staying connected? (I once had this problem with long speaker cables to a second system, and the only solution I found was to install knife switches and just live with the noise when I wanted to run the remote speakers. But that was many years ago on a cheap receiver.)
Even expensive stuff can have a cold solder joint at the connector which acts as a rectifier, making the radio station audible. Also just try cleaning the plugs and jacks. Or try different cables; internal oxidation can be at work.
Ground runs can possibly solve this problem, unfortunately you will have to experiment for yourself. Begin with the tonearm to phono stage, add a ground, or if it already exists, remove it and listen. Run a ground between the preamp and phono, without the turntable ground, and with. If any equipment, especially the turntable or phono stage are sitting on ANY type of metal stand or rack, run a ground from the rack to a true ground. I cannot promise any of this will solve the problem, but it is only an exercise in labor, with a small investment in some ground wire. I sincerely hope one of these suggestions will bleed off your unwanted radio reception.
It could be a ground loop created by having your basement equipment plugged into one electrical circuit and the stuff upstairs on another. Perhaps as a test you could temporarily run an extension cord down to the basement so that all of your equipment can be plugged into the same electrical source.