^It's very unlikely there's only one grounding cable. My Accord has 3 or something from the Engine/Tranny.
I'm obviously no expert, but guys with big sound systems that draw a lot of current, all the lights would flicker with the subwoofer firing, and this was largely due to faulty grounding.
I'd look at Element specific forums, and find out what the locations are.
But then again it could be something entirely different.