Turntable Hum


I've got an old Technics that is giving me fits...there's a slight hum present, that's there regardless of whethter the unit has a headshell attached or not, and regardless of whether it's AC power is plugged in. When I swing the arm across the platter, the hum varies from crackling and loud to nothing. It's not near a transformer or anything like that. Any ideas? I'm really perplexed by the behavior of the arm.
vanmeter
Could there be a problem internally with the arm wiring, it seems that a hum from a broken or bare wire might change it's sound when the arm is moved and changes position. Just a thought.
What cartridge are you using? If it happens to be a very high output cartridge like some Grados, they can cause hum.
I have a Stanton 500, a Shure m97xe, and a Shure v15VMR, and the hum is there on all of them...but it's also there without a headshell attached. I'm afraid it's the wiring in the tonearm as well, but I feel reasonably comfortable attempting to replace it. Is doing that something that will cause me to pull my hair out? It seems straghtforward enough.