If it's truly pinging or knocking and you're actually able to hear it then I doubt bad gas or environmental factors are the issue.
So bottom line is this. If you're hearing a real knock then your car is not picking it up and making the appropriate adjustments to correct the issue. That would mean there is another issue with the ECU or knock sensor which would need to be addressed at the dealer. It seems like a faulty sensor would generate some sort of code. Take it to the dealer and have them drive it to see if they think it's really knocking. That or test drive another car and see if it does the same thing. These engines are exactly quiet under WOT when it get above 4k rpms. They're pretty loud.
Old thread, but I got to searching about foam insulation around knock sensors. My '13 has a foam insulation under the lower intake that pretty much fills the whole knock sensor valley and the pics I'd seen of Z28th1s's manifold swap...didn't have anything there. You could see his knock sensor valley in the pic. MAYBE it's there for simply cancelling out some engine noise but maybe it also has a dual role of isolating the knock sensors better to detect knock?? Just putting that out there. I've seen on other platform forums that a few people were saying this. I don't know if it's correct or not but it seems it might isolate ambient noise to an extent so the knock sensors could detect the knock frequencies transmitted through the block better. Sound like a possibility?
Anyone else have the foam under their lower intake? I might need to start a new thread.