Warble Often associated with Stratitis however there is another kind of warble (sounds like flying razor blades or a chain-saw) that occurs mainly a plain G string and sometimes on othert plain strings. The severity of this warble seems is connecteds to the degree amount of midrange scoop the pickup has, more scoop means more warble.  It's cause remains a mystrey but I hypotethize there are naturally occuring warbling tones in every string but midrange complexity masks it over. That's why the warbling appears worse when the midrange is very scooped transparent. It is very difficult to get rid of since it is not related to proximity of magnets to strings.