If your old pickups were not humbuckers, they probably weren't as "hot" which means there is a lot less buzz or static noise, this isn't always true though. Humbuckers tend to be a higher output, or "hotter" than single coil, so they naturally tend to buzz a bit more.
But like everyone else said, check your grounding and make sure that they all lead to a common ground point.(you need to ground your pickups, pots, switches and your jack)