Static versus poor grounding?

What case are you using by the way? A completely steel case? Which PC component has a live connection connected to your case? Most electrical wires should be shielded away from the surface of the case it touches.

Most components will rely on the PC case for grounding as well besides using the house grounding via the PSU. But of course that is not the normal practice as if you would need to rely on 1 source of grounding, there is a load difference between the house ground and from your electronic circuit grounding.