I agree with herman, you need to use a sheilded cable for the phono interconnect. Your also losing some transparency and detail as the EMI and RF cause a "haze" over the sound that you don't notice until the cable been replaced. Look at any dedicated phono cable and you'll notice that their all shielded for this reason. If your not running a ground wire from the tonearm to the preamp, I would try this first as this may rid the specific hum you describe, but your still left the EMI/RF issue. With my TNT/JMW10 I have never needed the ground wire when used with a shielded cable.
If you like nordost cables, the expensive quatrofil is sheilded and would be excellent as a phono cable. If your looking for an inexpensive alternative I have a Discovery interconnect, that I was using as my phono cable up for sale on Audiogon (no, not the reason for the post; well, maybe a little) for $100 but for a fellow VPI/analog guy I'll drop it to $75 with free shipping. I'm currently using Silver Audio's silver breeze(dedicated phono cable) which is excellent and highly recommended. Yes, it is better than the discovery cable, but goes for $400. Check out their web site , Silver Audio.com. Happy listening