Carver A-500X picks up stray radio stations

Hi, My carver A-500X amp picks up stray radio signals. It is plugged into an outlet with no oter cord plugged into that circuit, although some ceiling lights are using the same circuit. The amp itself does not seem to have a grounding screw, nor is the power cord grounded. Can I just connect any cable to one of the external plate screws and ground that cable? Is there any other solution to the amp picking up stray radio?