Make sure all your solder connections are good.
Then if it still does it I would start remove things from the circuit and isolate things.
I would go as far as wiring one pickup to one pot, or just one pickup direct to the jack.
You can do that and control the volume with the amp controls.
However much you isolate, be sure and keep the bridge grounding wire grounded to something in the circuit.
Actually I would make sure you have the bridge grounded first.
Hollar back, and tell us what you find, and if you can't fix it we will go from there.