Your grounding is likely just fine, 6" away should be close enough to on the terminal. When you say noise, are you hearing it go up and down with the engine RPM's? If so then it may be a low pass filter that you'd want to look into... heck for extra nerd points you could build your own, I have a feeling there's a picture of one up here somewhere.
edit: not a picture, but a link to some more threads http://www.risingsun4x4club.org/foru...ead.php?t=9852
82 fj40, 99 uzj100, 06 gx470
05 525EXC, 01 XT225, 07 TTR90, 07 CRF50