I recently bought a "previously-owned" 5-string with active pickups. Not being familiar with 5-strings, I can't figure out why the B string isn't as loud as the other strings. For example, when I play a 5th fret E, the volume is much lower than when I play the open E string. I'm thinking they should play at pretty much the same volume. Is this a pickup problem or is this something common with 5-string basses?