Where Peter Walker is spot on, is in saying " We listen to funny noises, funny distortions, and see whether these things are going to matter, to get a subjective assessment" - that's exactly what I do, my ears are pricked up for "funny noises, funny distortion". The difference is that I do it "deeper" into the presentation - the type of thing people call the signature of a system, its "sound", the qualities that cause them to say they like one component, and not another.