Hey guys thanks for the replies.
I have a stock cat, and he actually though that might be one of the reasons for the knocking, he did ask me to get a highflow and take it back for a re-tune at no extra cost.
R31Nismoid, I got a 38mm external gate setup (Tial gate) and the 3037 has a 0.63rear avo rear housing, and I'm hoping that the cat is the problem behind the knocking, but as for the cold start, I'm hoping he will give it another go and fix that problem too.
The other thing I just remembered is that I dont have an oil catch can, they plumed it back, would this cause any knocking?
It probably wont show much but I added a pic below of the setup.