I'm speaking from personal experience.
My car used to ping at anything around or above 4000rpm, some days it would, some days it wouldn't.
Being the stubborn and over enthusiastic child I was, I kept going, pushing it and driving it with the "she'll be right mate" attitude.
One day it started blowing smoke, then abit more, then abit more - till the motor died!
And guess what? This was a STOCK engine! Except for a Cat Back Exhaust and guess what else? Front Mount Intercooler (800 x 300)
What I suggest to you, check your injectors or get them cleaned straight away, check the timing, it may seem it's not touched but a careless belt change may have knocked it out.
I have a new engine now (RB25DET) and with Full Turbo Back Exhaust and Front Mount Intercooler I have not heard one ping whatsoever.