It seems like there is something wrong that simply changing from plastic to glass cable is not going to fix. I have had the same issue intermittent. I could never figure out exactly what was causing it but mine was very loud not just faintly a part of the music. I was thinking it was some kind of interference from another cable or source but I don't know exactly. I'd say to try and move you cables around and see if it helps before buying any new cables.
