If the buzzing is not as loud when you touch the strings, there's probably a short somewhere in the wiring of the guitar.....as for the single coil pickup buzzing louder than the other pickups, it alway's will. The humbuckers are 2 single coils put together that cancel the hum, that's why they call them humbuckers. There will alway's be some extra noise the louder you crank an amp with overdrive, a noise gate may help some.