Hello chaps. Just an update. I ended up fitting the old ones back. The kit was from the states - an ACdelco kit which is a gm brand as im sure we all know. That lump is used quite extensivley over there in all sorts of cars. Dusted off my vernier and measured them all up in every way as best i could - absolutely couldn't find any difference in any way. Its annoying to do a job and not discover why something happened, goes against my better instinct but my chum needed his car back so that was that. Old ones went on and its now as quiet as a mouse. It shall remain a mystery......
Thanks for your input tho guys