If you twist the plug, can you pick up NPR?
It sounds like you may have a grounding issue. Does it happen when the adaptor is not plugged in?
Does it happen only when the ethernet cable is plugged in? Try a new shielded ethernet cable. After that, what access do you have to the wiring for ethernet or access to the router? You could try connecting the ethernet cable directly to the router to see if it's wiring in the walls...