[cattzap]

A hum is usually a shielding issue. Not a ground issue. There is a very good chance that your guitar is picking up rf noise that you cannot see, that was not present in your previous location. Very few guitars are properly factory shielded. Use an ohmmeter and see if you have continuity from the bridge to the outside part of the output jack. I would be surprised if you did. You can get shielding tape from Stew Mac. Remove the strings and clean it then cover every spec if the inside of the cavities and the entire back of the pick guard. Make sure everything is connected to the ground lug of the guitar. Including the tape. This may mean that you need to add a wore with an eye screwed to the body so it it touching the tape.

As this is an acoustic place, the same thing applies, only it's a little more difficult to accomplish. You can wrap the outside of the wire going from the pickup to the preamp, and you can cover the outside of the preamp with the tape. If the battery is not inside the preamp, wrap its wire and cover its little box. Then make sure all of the copper foil tape is connected together and to the ground lug on the output. It's not an easy job because of having to work thru the sound hole, but it can be done.