I'd been having a pinging issue for a while now, and after having the engine rebuilt, i thought it'd have to be gone, for sure!
Unfortunately, i still have to run premium to stop it from pinging. I have no idea what could be causing it. Everything else seems to be running fine now. :/
There has to be some fault with the fuel/air mix or something that is causing this. My car doesn't quite feel like it's ever hit 35mpg (although it keeps tempting me to change down, and i am weak), and the top end power feels a bit off. :p