An update:- Bought some new Raceface cranks, new chainring and fitted the Raceface bottom bracket that came with it. I also fitted a new chain as well.
Definitely feels much smoother. However, I'm still getting a little bit of noise still. Could it be the chain just stretching out as it's new? Back wheel feels good, noise only happens under load. Only other thing I've thought of is hairline frame crack maybe? I've check the bottom bracket area, it all looks good.
Completely mystifying, It was silent until I struck the cranks. Anyone got any thought?