Moving magnet hum

Yeah, we bought a hamster, and he's hard at work running on the wheel which drives a flashlight bulb.  Tesla told me about it.

By the same token, I have some older AT's that don't have a ground tab.  Back in the dinosaur era, I used to own Shure V15s... Don't recall any of them having a ground tab.  But we didn't have electricity yet back then, either.  So I may not have been able to see the tab by candle light.

To the best of my knowledge, only a very few cartridges have one of the two "ground" pins connected to tonearm ground and hence to earth ground.  Decca and early Grado come to mind.  Certainly there may be others. So, Yogiboy, what "ground tab" are you talking about? I respect your fund of knowledge, but I am confused.  Sounds like the AT150MLX has a ground tab(?)

Most cartridges don’t have a “ground tab”. The 4 pins are used as hot and ground, respectively, in each of two channels in a SE connection.  But in a balanced connection to a balanced phono stage, the ground pins deliver the negative phase of the audio signal. So your grounding problem probably lies elsewhere unless one of those pins you’re using for audio ground in an SE connection is loose or disconnected. Check that but also look at the external ground connection between phono stage and TT or tonearm.