@converge Hi there - Yes, I had a ugly situation from my neighbor who had a very illegal CB radio with a high power transmitter. It was bleed into my stereo to the point I could hear the conversation. Through process of elimination, I fixed it by using coax for my speaker cables. I used two of them, grounded the shield to the chassis of the amplifier, which was Earthed, and using the center conductors of each to carry the signal to my speakers. The speakers were Dahlquist DQ-10's and the center conductor the coax was 16g. The shield was a heavy copper braid. Unfortunately, I don't recall the brand name of the cable. Over the years they disappeared somewhere in one of the moves.
What I suggest you do is put some ferrite cable clamps on the phono cables. Since they are coax, they won't affect the audio signal but should squash the RF floating on the cables. The word "some" here means three or four spaced evenly about the cable run. Use a thicker wire on your chassis ground for the phono. It won't reduce hum but it does make a lower impedance path to earth for RF.