That is the question. I've left a blend pot case ungrounded before with no problem. And, at other times, I've grounded all of the pot cases. I've always used the 'star' configuration - separate ground wire from every component and case, brought together in one joint. Just read an article on Best Bass Gear about leaving the pot cases ungrounded, so I removed the pot case grounds on a P-bass type Yamaha (RBX250F). I still have the buzz which is most noticeable with tone knob all the way to treble. Goes away when I touch any metal part. I've checked ohms everywhere. Everything is grounded to 0.2 ohms or less. Still got the buzz. Is this an issue with the stock Yamaha P-type pickup?