from my experience data logging and having my car tuned.
0 knock is ideal, but you will never be able to get it like that 100% of the time.
this is due to several things i have come across.
1. bad gas is the main culprit for me. i use the same gas company and same gas and i can have knock of 3 or 5 one time and the next fill up, a 0 knock reading.
2. i have heard that our dual knock sensors are very sensitive and therefore, will register false knock at times too. either engine noise or whatever.
i will say again that this is just coming from my experience and i am in no way an authority on these things.
more than likely thats it.
try putting about 4 or 5 gallons of race gas (103 unleaded) to a half tank or so of regular93. and that should bring your octane up if the gas is bad.
dont run your car too lean on the diablo or the race gas will make it too lean.