I have a one-pickup lap steel with volume and tone pots. I have tried wiring it and re-wiring it and still get a pretty constant hum that does not go away when I touch the strings. Yes, I have a ground lead going to the bridge. I also have shielded the back of the pickguard and the cavity and made sure the foil overlaps. My multimeter says I have continuity at all the grounds. Any ideas? Thanks in advance.