The nature of a volume pot is that when turned fully down, the signal connects directly to ground so that it is impossible for the signal to pass through.
If you are still getting a signal, there is either something wrong with the pot that is preventing to from rotating fully to the 0 ohm position, or you have improperly wired the ground. Check to make sure that the ground from your pickup has good (0 ohm) continuity to the 3rd leg of the volume pot.
If that doesn't help, try cleaning the pot.
All of that star grounding nonsense is pointless.
Your bass has only one ground, at the output.
Ground loops usually occur between equipment connected to different grounds.
Technically it is possible to have a ground loop in a bass, but it is extremely insignificant, and will not cause any issues.