I can conclusively prove that some cables sound different. I have a lovely 3m RCA cable used for my subwoofer that I recently replaced. Even in a double blind test I can pick the one cable from the other under the right conditions. The right conditions being that the old cable, when getting near to my AVR's power cable, would cause the sub to hum very badly. The new cable does not. The new cable probably cost less than the original one that hums 
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I would suggest that the old cable may be damaged. Also, one or more of the plugs may not be making intimate contact with the socket
Many cables brought to me can successfully be fixed by unsoldering the plug, cutting off a few mm of the end of the cable, cleaning the plug and resoldering. Is also possible that the original soldering job was dodgy on account of the metal being dirty or corroded. To achieve a 100% soldered joint, both surfaces must be pristine
Then you get mechanical wear. This is often apparent with mobile phone charger leads, as people are a bit rough with it or else detach it from the phone using the cable and not the plug. The copper strands inside are usually extremely thin and copper is not a strong material
To explain cable damage a bit more, the shield is usually wrapped in a braid fashion, as can be seen from this image
If the cable is bent over a sharp corner, the braid can separate and allow in the hum through induction and exhibit the symptom described
(An induced current (the hum) can be created in a cable lying adjacent to another carrying current with the collapsing magnetic field due to the 50Hz AC travelling through - this is how transformers operate)
