Earthing the Canbus

[GSwadd]

I have recently wired my Zumo through the BMW canbus power power outlet near the steering head on my 1200GS but seem to have a bad case of ground loop syndrome through my Starcom when the Zumo is plugged into it. Before it was wired directly to the battery just like the Starcom. From a bit of research it seems I have two options - one to return the wiring as it was to the Zumo and the other to earth the Zumo back to the battery. Does the Canbus only supply power and all earths still go to frame and therefore battery or are things earthed back through the canbus for some reason? Will it hurt to take the Zumo earth lead back to the battery and leave the power on the canbus?

Awaiting for someone to tell me I'm an idiot and just do it...