epiphone eb0 humming problem

[Twincam]

When I touch the strings or indeed any metal part of the bass it induces a hum.
Could someone explain the cause of this and how would I go about fixing it?. I'm not afraid to get stuck in there with a soldering iron etc even with only my basic knowledge if someone can give me clear instructions.
I've had a look inside and all wires seem well conected.

[Dazed]

Does it look like the wiring has been messed with? Sounds like an earth problem

[icastle]

It's an earth issue.

Make sure the wires connecting the pot cases are well soldered and watch out for the wire that appears underneath the bridge - if that's broken (or even loose or dirty) then that'll cause the earthing issue you describe.