My understanding of the new engine is that the inlet valve is kept open on part of the compression stroke.
Is it possible that the ignition is so far advanced that its firing before the valve is closed
The noise I get with the higher octane could be described as "induction noise"
Definetly not.
A firing with open inlet valve would mean a dramatic lack of efficiency, gas has to push pistons down AFTER the end of compression.
Leaving the inlet valve open a little longer just reduces the amount of fuel / air charge in the cylinder and effectively reduces compression ratio at lower revs (and because this expelled charge is stored in the manifold to be sucked in next induction stroke = lower fuel consumption), if the ignition was so far advanced that the charge was ignited with valve still open the piston would not yet be third of the way up the stroke - the result would be flames in the inlet manifold and maybe an engine on fire as the rising piston pushed burning charge into manifold and beyond.