I have 4 Jazz Basses, all have traditional Fender Pickups: a `78 Jazz, a US Vintage Series '64 Jazz, a Noel Redding MIJ '65 Jazz and a MIJ '70s Jazz with CS '60s pickups. I assume that all of the instruments are grounded properly. The '78 and the Noel Redding make a loud unwanted noise if I accidently touch the pole piece under the E-string with my thumb, the others don't. I remember when I first tried a Fender Jazz long long ago (a '62 Vintage Series) it made that unwanted noise, too. The shop-manager looked a bit puzzled, but I simply never had to care about not touching the polepieces with my thumb on my Yamaha BB and other basses I've tried, so my technique wasn't prepared. What is the reason for the noise? Why doesn't this happen on all Jazz Basses with passive single coil pickups?