If this is any chance a Grado cartridge, they are notorious for hum. If you post your Table and cart models, it would make it easier to give a good answer. I have several Marantz (6100 6200 etc) all have ground wires. I suspect it would be easy to locate the ground point inside the table and run a wire. When I am messing with them I use a long piece of 20awg with alligator clips on each end. Clip one to the ground on my amp or pre then poke around on various grounding possibilities in the table till I get the best results. Be careful not to short out anything hot though.
How to ground old turntable with no grounding wire
I have an old Marantz turntable that I want to start using again. I have a terrible hum through my speakers when it is turned on--worse when the tone arm is on its rest, better when it's over or on a record. I'm guessing it needs to be grounded (although it was never grounded when I used it years ago). But, it has no grounding screw or wire that I can locate. Suggestions? Any ideas for other causes of this new hum? The other thing I'm wondering about is electrical polarity, because it has an old (non-polarized) plug, plugged into a polarized extension cord. Any and all suggestions welcome!