I have a Fender P bass. It originally came with a metal pick guard and sounded great. When I swapped the pick guard out with a plastic one, it added a low level hum noise. So, I attributed this to a difference in pickup shielding. My thoughts it raised the noise floor and gave me less dynamic range. I noticed that the cavities looked like they were painted with a black shielding type of paint. I shielded all the cavities and back side of the plastic pick guard with copper foil (better effective shielding). Afterwards, no hum at all. It sounded great, end of noise problem. Question - If a bass does not have a pick guard to provide additional pickup shielding, will it have a higher noise floor and tend to have low level hum?