Sorry for the delay reply. I wanted to try some 91 Octane....
Same thing, same ping. 87, 89, and 91 octane. I'll see if I can hear it do it in the drive this weekend, but I *think* it only happens under load and modetate to strong acceleration. At least in the lower 3-4 gears (auto tranny). SO hard to record. But I will try it.
It is kind of a ping or rattle. Might also be something loose. Again, I have only had irown block engines in the past, so I have no frame of reference to a knocking sound in an aluminum engine.
I plan to drop it off at the dealer next week. I'll let you know. Thanks!
(I will be annoyed if it is knocking. My Nissan takes any Octane in its V6 and does fine, even though it RECCOMENDS 91... and it has 211k miles now also.