Martin Little Martin A guitar pickup is basically just like an energetic mike coil. For decades, energetic microphones have now been wired with the voice coil mounted on the primary of the microphone's transformer, and not referenced to ground (‘floating'). The microphone's case is normally linked to the cable guard, which is connected to the microphone amplifier's soil (see Rane's site for more discussion).
By and big, vibrant microphones are extremely calm units as a result of the combination of transformer isolation and healthy, flying transmission lines during, along with shielded, humbucking coils.
Therefore why don't you instruments? Instruments are notoriously affected by noise. Humbucking pickups are only a partial (though essential!) solution. Well-known solution is to move your guitar pickup to a balanced result, just like a microphone. The same strategy was printed this 2001 patent application like this Martin Little Martin?