If you experience hum and that hum stops any time you touch different parts of the TT, tone arm, metal deck, etc., even though you may and should have your TT grounded, run some additional wire or wires from the point(s) that you touched when the hum abated. By this, I actually mean, properly secure your TT and invert it, giving you access to the underside and attach spade connectors to a piece of wire and loosen a screw on the underside of the TT, slup the spade connector in and re-tighten the screw(s). Run this second or third wire to the grounding post of your phono preamp and that should eliminate any hum that might have been originating from the TT. Sometimes people use carbon fiber tone arms, as specially longer arms, and the wires that are contained inside of the tonearm are not insulated, may pick-up RF or electrical magnetic fields, because the carbon tone arms are transparent to these forces and do not provide the shielding that a metal tone are would have provided. Secondly, some areas or installs may be more subjected to these forces than others are, or some interconnect wire runs may be longer than others and you are using RCA connectors (not balanced cables), you should look at double shielded cable, which you can obtain at blue jean cables.