FWIW this could also be occurring at the output of the phono stage. I would at least try a different set of interconnects at the output of the phono section to see if that had any effect.
RFI can be really pesky. A phono section that picks it up can wind up being shipped back to the manufacturer for repairs, so usually some effort is made to prevent it happening. But not all designers work with the same tool kit! Several things affect RFI:
RFI injected at the input. RF beads can be installed to prevent RF getting to the input section if it makes it past the input connector. If the phono section is lacking 'stopping resistors' it can be prone to this sort of thing since the input device (tube or transistor) can then serve to rectify the RF, causing it to become audible. Stopping resistors can cause a Miller Effect high frequency rolloff, preventing RF from entering the gain stage. Don't worry if you don't understand what I've written, but if you send the unit back for repairs, point out this post to the manufacturer.
RFI introduced by poor grounding. This may be as simple as a bad power cord or a loose screw in the breaker box. Poor ground does include the grounding scheme of the equipment as well.
The thing is, we're likely looking for something that has changed, since this problem suddenly showed up. For that reason I'm suspicious that the cause is outside of the audio system itself; IOW I think its a bad ground.