At about 3500rpm driving steadily i can hear a weird metallic noise from the front of the engine bay. The best description i can think of is that its like someone pushing a wire brush along a piece of sheet steel very smoothly, or a bake bean tin full of 3/4 inch panel pins being rolled steadily.
I know what most of you will be frantically typing - pinking, detonation etc etc etc etc. BUT Its only started doing this since i fitted the bigger SBD manifold AND i turned up the fuel pressure to where it was before followed by another 20 psi, and went round the block for several tests. So ive ruled out pinking. The pressure is now back where it was as per the rolling road day.
the noise starts about 3500rpm, then phases out at about 4000.