Single coil is known inheritance of the 60 cycle hum. You can't shield that 60 cycle hum, no matter what u do u cant get rid of it, but u can definitely reduce it. I avoid using single coil due to this noise problem. Either u change to a full humbucker or a stack single whereby you still get the single coil sound with 2 coils stacking up each other like a humbucker.
1 way to effectively reduce noise is to shield your pickup cavity, using a carbon conductive paint or a thin copper strip or aluminium strip with conductive sticker. Sheild ur pick guard too.
1 more tip is, don't adjust or expose ur pickup height to much above the pick guard or the body cavity. The higher the pickup magnet expose on the outside of the cavity or pick guard, the higher chances ur pickup will pick those EMI noise.
This is 1 reason on why guitar design with a lower deep neck pocket(the connection between the neck and the body where the metal plate is) is a better option. It's because u can get lower profile action and lower pickup height adjustment and the result is in turn lower noise because your pickup is way inside the body cavity or pick guard.
Another is, you can shield ur pickup with the copper strip all around, but there's a disadvantage of doing it, the pickup will change tone or make the tone dull due to the copper strip surrounds it disturbing the copper coil inside.
Regarding your pickup selector switch, what u can do is loosen abit the tension of the spring attach to the selector switch or totally remove the spring or change to the selector switch to a non spring type like the 5 way super selector switch spoted in Ibanez guitars, It's the switch spring that creates the noise and in turn picks up by ur magnetic pickup.
Don't understand reading this, try to understand it, kekekekeke
