Hi ConorB.

re: humming; Probably a ground (earth) issue. Did you run a wire from one of the bridge posts to a common ground?

As for the switching problem, yes, most likely a wiring problem. (could also be related to the ground problem)
Post a (clear) pic here of your control cavity and switch cavity so we can see the pots & switch wiring and it will be easier for us to diagnose.