Humbucker pickups were designed to eliminate hum. Traditional single-coil pickups are prone to hum, but humbuckers are wired with opposite polarity to counteract the noise. Traditionally, Les Paul guitars have pickup covers, while humbuckers on guitars designed in the superstrat style are exposed.
Humbucker pickup covers come in chrome, silver and even gold. Covering your pickups with a polished metal cover can improve the look and value of your guitar. If you have installed vintage humbucker pickups in a new guitar, they may look out of place. Using a cover hides this.
Pickups can collect dirt and grime. A cover keeps these contaminants away from the inside of the pickup and prevents build up. A cover also protects the pickup from the pick of the guitar. Although the strings run above the pickup, it is possible to damage an exposed pickup with an over-enthusiastic picking style.
Pickup covers add a dimension of shielding that reduces interferences and hum. At high volumes, even the highest quality humbucker is prone to making unpleasant humming sounds. The layer of metal covering shields the pickup from the strings and reduces tendency toward hum.