I assume there's not corrosion on the conductors and the insulation hasn't been caught instead of the conductor? I believe the the US still have zones and recommended depths, if anything has been drilled into the wall inline vertically or horizontally that could be point to check out. Otherwise you may have a join that's been disturbed.
What type of wiring is it? In the UK we use pvc insulated and sheathed cables plastered in domestic properties. Is it timber frame and can the cable be pulled through the timbers or through a conduit? You might be able to trace the route that way.