How u do the grounding? kindly follow accphoto's way of ground... besides, check your volume pot's shaft's grounding whether your sfat n the chasis is touching, normally it should touch...
In this case i will sugget to do something on the grounding to reduce the hum 1st,even using RC filter the hum sound also can be reduce by proper grounding,then change to choke for further improvement.
1) ensure the contact point of the volume port to the chasis is connected, may need to remove the paint on the chasis where the volume pot shaft is srew on the chasis. (if the volume pot & chasis not connected, while at minimum volume setting it will has a lot of noise)
