Hi Chris,
Go to Wikipedia and look up ferrite cores. The graphics shown in the writeup show how the ferrite core is used.
1. Do you need a core on the power cord? Probably not. The key is to add one core at a time and note the effect on the sound. That is, is the RF or EMI is eliminated.
2. Start with the turntable ground wire. Insert the wire between the core now reattach the wire between turntable and the phono section.
3. If this eliminates the noise then you don't have to do anything else. If this does not eliminate the noise. Try attaching a ferrite core to the left and right connectors of the tonearm interconnect. Does this eliminate the noise? If not, try a ferrite core on the power cord. of the phono preamplifier or the turntable motor.
4. Continue this process until the noise is eliminated.
Hope this helps
Etbaby