I have a VPI Scout with the same tonearm with the valhalla wiring. When I first got it I had a terrible hum even with a ground wire hooked to the ground on my preamp when using some nice silver interconnects. I ended up purchasing some shielded silver interconnects and the problem is now gone. My interconnects are custom made by a nice fellow and I contacted him about the hum with the interconnects I got from him and here is what he said/did for me:
"That interconnect (that I had purchased from him) is a replica of Kimber interconnects ( braided) If you send it back to me I will place a copper braid over it ( and recover it with new nylon braid) I will float the braid ( grounded at the turntable side and open at the pre side) that will get rid of the hum."
He re-did my interconnect as he described above and no more hum.
Hope that helps somewhat.
"That interconnect (that I had purchased from him) is a replica of Kimber interconnects ( braided) If you send it back to me I will place a copper braid over it ( and recover it with new nylon braid) I will float the braid ( grounded at the turntable side and open at the pre side) that will get rid of the hum."
He re-did my interconnect as he described above and no more hum.
Hope that helps somewhat.