You could try ferrite ring(s) and wrap the phono cable through it several times. This is a easy fix if it works. Also, you can braid the cart. leads of the tonearm prior to connecting to the cartridge pins, but be gentle.
If there was a phono RFI/EMI issue I've had it or have it. I can't use a SS phono preamp in my system. I'm just glad I found that tubed phono's defeat most of the RF/EM issues I have. I still have issues but they are manageable now.