Ive got a strange noise at around 3KRPM sounds like what knocking has been described to me as, however it seems to do it religously and only at 3k and the knocklink shows nothing. anyone got any ideas ??

Its either the wastegate valve chattering against the turbo housing as it starts to open, or a cracked heatshield. If you get the sound at 3k, without using boost, then its the heatshield.

The most common heat shields to fail are the one on the manifold, where the two banks meet (driver's side at the front) or the shield around the standard up pipe.