Another "kinda-newbie" head scratcher

EMI is a term usually used forr electromagnetic radiation from a motor/ generator or can happen in the rectification of AC to DC, occurs inside all our gear or probably also during inversion of DC to AC, as in a car. It can cause noise either through the air or by traveling on wires. RFI is also electromagnetic radiation, usually travels longer distances at high frequencies but is otherwise similar to EMI. If you’re hearing radio broadcasts, that’s clearly RFI. By all means if you are using unshielded cables try replacing them with cheap shielded ones just to prove the source. Morgami make good ones that are inexpensive. Also you might try the RCA plugs for unused jacks that I mentioned. Also move stuff around and observe the results up or down.

I agree with @audphile. One of the small clips wired to the cartridge pins could be making poor connection.

If you have a detachable headshell, there could be poor contact between the pins on the headshell and the tonearm connection. This has happened to me.

The shield of one or more cables might have been disconnected internally. You will need an ohmmeter to check this or you could inspect visually. Remove the cap on the RCA connector (screws off) and visually check connection. You could gently prod the wires to see that they are firmly connected to the plug. 

It would be good to check out the all connections from the cartridge pins all the way.to the input of the phono preamp.

You can also test each cable independently by replacing one at a time and checking for noise.

Also check that the ground on the phono cable is firmly connected to the phono preamp ground. Break and remake connections.

Of course, do not have phono preamp or line level preamp power on while making changes. Turn power on only after all connections are made and checked.

Happy troubleshooting!

Any wall wart in the area? Just might be the culprit!

@retiredaudioguy it stopped! I thought I had tried that before to no effect. But just having the turntable disconnected, eliminated the noise. Huh. I have Cardas phono cables on now, they replaced uber expensive AudioQuests when I first noticed the problem. 

My condolences. You have a frustrating problem.