You see the human wave at the stadium? Everyone is at their seat but the wave propagates forward. This is how music propagates down the wire. The electrons are not going anywhere but we hear music. At the stadium, there are big guys, small guys, thin guys fat guys, some standing and some walking. These are noises and that is why we never see a perfect human wave. In cables, the electrons are boxed in. Some electrons can move freer than others; some ran into obstacles (impurities) and some forced to move in different directions (external interferences). These are noises as well and that is why we don’t get perfect music. And that is why we get different sound using different cables.
Make sense?
Make sense?