I think you need to find out if the rf is being picked by the amp or preamp.
Do you still get noise if you connect the Wadia directly to the amp?
If so, then it's most likey the amp is picking up the noise. Tube equipment tend to have very high input impedance whcih makes it more sensitive to rf pick up. Unfortunately, ferrite core won't work in this application since the frequency of the noise is too low. You might have to add a low pass filter at the input of the amp to filter the rf noise. See if the noise goes away if you short the input of the amp with an RCA plug. I think you really need to isolate the componet that picking up the noise.
Do you still get noise if you connect the Wadia directly to the amp?
If so, then it's most likey the amp is picking up the noise. Tube equipment tend to have very high input impedance whcih makes it more sensitive to rf pick up. Unfortunately, ferrite core won't work in this application since the frequency of the noise is too low. You might have to add a low pass filter at the input of the amp to filter the rf noise. See if the noise goes away if you short the input of the amp with an RCA plug. I think you really need to isolate the componet that picking up the noise.