Actually surface oxidation can change electrical properties of a cable. When you chemically change a substance to a different one, it changes properties entirely (including electrical). I don't know if rust is a good conductor or even verdigris for that matter, however, the exterior of the cable changes into verdigris (that much is confirmed), but we don't know how deep the surface goes. It may be variable. This changes the crossectional area of the cable, thus changing resistance due to this equation:
R = p (l/A)
-R = electrical resistance
-p = Resistance constant for the certain material (normally shown by the Greek rho symbol, but a p looks similar to the rho).
-l = length of the cable/metal/material.
-A = crosssectional area of the metal/cable/material
When the A is decreased (due to the surface changing), the resistance goes up. Depending on how deep the reactions go, your resistance gained may vary. I don't see this change being that great though (not audible at all unless you go through some sort of advanced oxidation that tears through the cable; then you have other things to worry about).
Although the electrical properties of the material have been changed slightly, I don't see it being a big enough change to hear sonically. It does change though.