I've got a Fender Custom Shop four string bass that plays like a dream, except for one thing. The 4th, 5th, and 6th frets on the G string are just dead, volume-wise and sustain-wise. The rest of the neck is pretty well balanced, even the rest of the G string above and below these frets. I've played bass for almost 30 years and had a lot of basses, and this is the first time I've encountered anything this noticeable. I'm not a luthier or anything, but I know how to set up a bass, and this one is set up well. I've tried different string gauges. The frets are in good shape and seated well. Anybody ever experience this before? Did you find a way to cure or at least improve it?