I just saw this and no doubt you've received answers. But in the likelyhood you have not, I have the answer.
Shielding. It's no more or less than this.
Most of the lower end Grado cartridges are not shielded, which is probably why they sound so good in their midrange. And the other have of the equation is Rega, they do not shield their TT motors. Hence, Hummmmmmm.
This is the problem. But there is an answer. Mu-metal. You may have been told about this. You can send away for this Mu-metal kit, $75, and you apply it to your TT and all humm or 90% is gone. Any remaining is very negligible.
I've been through this whole process so it's not hearsay or conjecture or whatever. It's honest truth. Repair techs as well as knowledgeable dealers agree and confirm.
Also, it's not only Rega tables, many others fit this category of having not shielded motors (or more specific, transformer in the motor section). I just experienced this same problem you are asking about with a grado silver cartridge and a Pioneer PL-550 TT. That wonderful humm.
The Grado actually sounds so good that I choose not to let the humm interfere with the good things the Grado produces. If you don't play music too loud it's really not too bad of a problem. But if you're insistant on keeping the Grado, buy the Mu-metal kit. You'll be happy. Oh, there's one other cure, and much better in my opinion, that is, if your system can take it--MC cartridge. Much better any day of the week than a MM cartridge (imo).
Hope this helps.
