I'll second both of the previous comments. Also, consider purchasing or obtaining a multimeter, and checking the cables for continuity from each pin at one end to the corresponding pin at the other end. And also checking that there is no continuity from each pin to either of the other two pins.
Also, your mention of the cables being non-shielded leads me to wonder if continuity is present between pin 1 (ground) at one end and pin 1 at the other end. I doubt that any reputable company would market a cable designed like that, and I suspect that if pin 1 were unconnected you would still hear something, but I suppose an open ground connection could account for differing behavior in your system vs. your friend's, depending on the design of the various components.
Regards,
-- Al