TC how is the idle? especially at start and when you come to a rest after a good run? on mine (with ITG) the vacumn pipe came off the brake assit unit, changed the noise (you could hear air being sucked in) the give away was the idle change though as it was leaking air into the inlet bypassing the ITG, other thoughts are knackered DV which is dumping air into the intake in a different way, when my PCV valve went oil built up in my DV and this changed the sound, just a few thoughts..........