Ground straping will probably fix that problem. I looked under my dash cluster and didn't see anything for a true ground, this makes me think the factory probably uses some rinky dink method to ground the cluster like perhaps a bolt or a screw that holds it to the mounting points. I had an old yota that had the same problem and that was the way they had decided to ground the dash gauges. I put in a real ground strap and viola, fixed for good!