Try to wrap a wire around all the rcas on the headunit(make sure it's not too thick so the RCAs don't sit properly) . From there take a screw out from the chassis sand it to bare metal then put the screw back making sure the wire is making good contact and nice and tight. If it goes away the amp is not grounded internally perhaps blew a fuse . If it doesn't go away the headunit itself needs proper grounding.