Hum is usually associated with stray magnetic fields usually from transformers in amplifiers or poorly grounded instruments or amplifiers. Shielding will help RF interference but will not reduce the stray magnetic fields that can penetrate all kinds of components such as the body, bobbins, pickguards, pickup covers etc. Using anything that will reduce hum such as Mu-Metal will also interfere with the magnetic path through the coil to the strings and change the sound of your pickup.