Cartridge, Phono Preamp Hum

I hooked up a new tt/cart/phono pre. Trans-Fi tt, Clearaudio Maestro Cart,
and a BAT VKP 10 SE phono pre.
I pick up hum only when the stylus touches the platter.
Played around with the ground on the preamp, nothing.
No hum anywhere else in the system.
I just installed the same cart in my set up with no hum. Try borrowing another phono-preamp to see if that's the problem...
Same thing happened to me about a year ago on a different set-up, except the left channel didn't work. Changed cables, switched cables, substituted different phono stage. Then I took the cartridge out, blew some compressed air over it, and reinstalled it. Have never had a problem since then. Was probably some dust (or perhaps the stereo gods were punishing me.) Try it. Might be that simple.
Turns out a ground wire from phono pre wrapped around one leg of the table then hooked to the input of the table speed controller has done the trick. No kidding.
Is the table made of metal?
I was going to add that sometimes a ground that is common to both the main bearing housing of the tt, the body of the arm, and the phono pre will fix the problem. But it varies from one tonearm/turntable to another. Some tonearms don't need a TT chassis ground, some will.

I find that some extra hook-up wire and a couple of alligator clips will allow one to explore the various possibilities of fixing ground/hum problems.

another thing; Some components that have a large transformer can cause some unwanted electromagnetic induction between the power supplies of other components. In that case simply moving the component with the offending transformer away from the component likely to be 'induced' by said tranny.