Hum/Buzz (grounding)

Seems like you have a grounding problem... I mean the wiring of your house itself. If your wall outlets have 2 instead of 3 prongs then there is no ground. You can't really do anything about it unless you stick a brass rod in the ground and connected your equipment's ground to it. I know it sounds funny but that's how house wiring ground is done...
Also, if you have several electronic equipment in your signal chain (amp, preamp, pedals, effects etc) try to connect them all on the same power strip. You might get a bit less noisy sound...
I am not of much help here but in the majority of cases, the house wiring is the fault.

 

Check the sticky for lyle caldwell grounding/shielding schematic. It worked on my basses.

 

I think you'll find its a problem inherent in how most basses are wired.

For more information, there's a discussion about it happening in Luthier's Corner: Mysterious Wire, or something like that.

Josh D

 

That doesn't mean you have ground though... it is likely, although it is also possible that the outlet doesn't have the actual wiring behind...
Anyway, as said above, the wiring of the bass might be the issue.

 

Here's the link.http://www.talkbass.com/forum/showthread.php?t=159191.
Trust me.
I've checked the very thing you have then when I used copper foil, and followed the guide lines using star grounding, I got silenced, or rather my basses did. No more having to touch the strings or knobs or bridge to stop the hum. It's a must read and do procedure and it costs less than $10 if you do it yourself.

 

Because grounding and shielding are separate concepts.

The ground just means there is a path from the pickups to the amp ground so you'll get current from your pickups.

Shielding is a means of dumping all potential noise to that ground rather than letting it pollute your signal. The Brits call it a "drain" rather than a shield, and that makes more sense (I think).

Grounding the bridge uses your body as a partial shield. Doesn't work very well, and it doesn't work at all if you aren't touching metal, but it's very cheap for manufacturers to do, and bassists are accustomed (conditioned) to it. Expect more from your instrument.