Something that's not often mentioned, but I believe is relevant here is the pickup aperture, or how much of the vibrating string that it sees; it's for this reason that single coils (with a narrow aperture) sound the way they do, clearly defined; whereas with wider aperture pickups, normally the situation with humbuckers, there's a wider mix of frequencies, giving the characteristic warmer or fuller tone. I don't know how they do it, but my Squier Jazz has no noise when either pickup is soloed, I have to assume it's a Fender noiseless 'single coil' design.