Ok so I finally picked up the BQS 3 band EQ for my 5 string bass that already has EMG P/J pickups in it. After finally getting everything to fit in the cavity I know have a buzzing noise whenever I touch the pickup housing. It's dead quiet otherwise and I never had this issue with the pickups with just tone/vol pots.
Sounds like a grounding issue to me... check your soldering joints on all ground wires including your imput jack.
Id say worst case scenario, get a cheap voltage meter and check all conections with that and make sure you didn't cross any wires or soldering joints anywhere. Its a good idea to put shielding and shrink wrapping on all wires.

hope this helps bro...
Well there are no grounds or solder joints, its all EMG solderless connections and actives don't ground to the guitar.