Earthing Problem

[sblueplanet]

I just acquired an Ibanez Mikro. Great little bass but Im having what is some sort of live hum issue. The bass has a PJ configuration. The back J pup is not affected, it just seems to be the front P pup. With the tone rolled off there is no hum with this pup either but it is when I introduce the tone I get that buzz whuch only disappears if I touch either the tone or P volume pots.
Ive already shielded both pup cavities and the control cavity so at a loss as to how to sort it.
Any help appreciated in advance!

[sblueplanet]

Update is that I just happened to set bass up for a look-see in my bedroom and when played through my practice amp, lo and behold, no hum at all. May still require some copper grounding wire put in under bridge and pups and attached to the shielded control cavity to alleviate completely if this is indeed the cause.