Potential Home Grounding Issue - Illinois
Turn off all the breakers, try them one at a time and see when the voltage returns, this should help to locate the problem area. Once you have the area found, turn on all the breakers, except  the breaker to that area, and check it again. Now with the problem breaker/breakers off, go through the devices and check if any have a bad wire. I would start with the switches that controls the outside light.