Robbie G has a Lian Li, not sure of the model. He had a ground loop problem, which I believe he managed to fix. I also had this with my Antec 300. With Antec cases, the entire front panel is encased in plastic, at least t is with the 300. Removing the ground wire was easy and solved the problem. With Lian Li, at least in Robbie's case, he had to remove the front panel section and isolate it from the case. Obviously, a much trickier job than just removing a cable.
I'd try a ferrite ring, as Auraomega said, see whether that solves the problem. If not, then you will either have to put with it, or do some DIY on the case.