I've replaced my hard drive cable twice now. The problem seems to be that the underside of the aluminum unibody has small ridges on it (you can see them, but they are small. The cable rubbed back and forth on these ridges, and you could see where the cable had shorted where it had worn away. It doesn't take much.
I found a youtube fix which involved only laying a piece of electrical tape along the underside of the cable (underneath the drive), and another piece along the body itself. A couple minutes and few cents worth of electrical tape later and all was working fine.