My 2004 Maxima 6 spd manual 75k miles recently started pinging with 93 octane gas. The pinging occurs consistently with moderate to heavy acceleration in 3rd through 6th gear in the 3-4k rpm range. Performance is still good with good power and there are no engine codes at all. I had the fuel system professionally cleaned and ran a couple of bottles of Techron injector cleaner with no improvement. Any ideas? - Thanks!