Mijo, I ask this out of curiosity, because you raise an interesting question: how many cartridge bodies are grounded or even can be grounded, unless there is continuity between the cartridge body and one of the audio grounds available at the pins? As you know, many cartridges are made of plastic or other non-conductive materials. Also, many headshells are non-conductive (made of wood or carbon fiber, for example), so grounding through the headshell is often not feasible. For that matter, the only cartridges that would be shielded would be those with conductive metal bodies that are then grounded preferably to the chassis. I am not implying that your advice is not good. I am just curious whether I am missing the point. Thanks.
This is not at all to say that you are not correct in guessing that the OP's cartridge is picking up some radiation from the electronic panel under the tonearm.
This is not at all to say that you are not correct in guessing that the OP's cartridge is picking up some radiation from the electronic panel under the tonearm.