I don't have a boost gauge fitted (other than the liquid gauge) but recently I've been noticing some strange behaviour. I'll be driving at part throttle pulling away slowly and the turbo will spool up really early as if there's much more load than there actually is. You can hear it dump boost sometimes too. It's very strange. I also think I'm getting overboost which is causing the knocking (which is now almost permanently if I give it some). Could the strange spool behaviour be the N75? It drives fine otherwise. I'm fitting a brand new OEM pump at the weekend in the hope that it might be the cause of the knock (lack of fuel).