I had the pinging issue when I was experimenting with 91oct Ethanol Blended fuel earlier this year, but when the the pinging became more prevalent - i went back to 93 only.
TODAY i began noticing the same rattling issue at low rpm's under load, and I've ONLY been using 93.
I'm going to read-up on the Cat-shield thing, and report back what I come-up with.
I HATE thinking my VVT is going to ****e.

I've had the VTC Rattle since I drove the car off the lot.
Oh - btw...I just rolled 69k. How about you guys???
Also - can anyone explain why this malody only occurs while you are underway/ engine under load?? --this is strange to me?!--
gr