This is read right out of my Owners Manual.
"You may notice light spark knock for a short time while accelerating or driving up hills. This is no cause for concern, because you get the greatest fuel benefit when there is light spark knock"
So, it's ok to have spark knock, as long as it benefits mileage.....what is Nissan's logic on this? Other text in the manual states that spark knock is bad. And most anyone has read how knock it is BAD for a motor.......hmm

 

A light spark knock is the equivalent to 'advancing' your timing, as the air/fuel mixture ignites earlier than normal. Emphasis on LIGHT though.

 

Define light spark knock plz.

 

Light spark knock is mild, barely audible pinging at partial throttle. It's kind of subjective, but if you've ever heard heavy detonation, you'll know what light knocking is.

Research has shown engines to be the most fuel efficient and to produce the most power when the timing is advanced to the point where light knocking is produced. Engines do not sustain any appreciable damage from light knocking at partial throttle, even over many thousands of miles. Knocking at WOT is cause for concern, though.