Uncontrollable audio feedback and effects owed to the unravelling of the turns in the coils are defects that the pickups can show even suddenly and some time after installation.
This problem can be solved by dipping the pickup in warm wax (potting), which removes up to 100% of air residue, and which is best left to experienced professionals. We recommend therefore that you do not follow this procedure yourself.
The guitar maker will boil water in a pot within which he will dangle (such that it does not touch the bottom) another container, in which he will have placed some sufficient paraffin wax. Once melted, it will be able to totally submerge the pickup.
When the wax reaches a temperature of roughly 60/65 degrees, the guitar maker will dip the pickup in, holding this too in suspension with a wooden handle which the pickup is hooked onto by its connecting wire.
Once the air bubbles have seeped out, normally within 5/7 minutes, the guitar maker will quickly extract the pickup, which is left to cool. The excess wax is wiped off with a cloth and later using a home (not industrial) hairdryer.