You need to bite the bullet and take it to your tuner.
Pinging sounds like gravel rattling round in a tin can so I doubt it's that.
Could be compressor surge. Is it at WOT? Or more at part throttle?

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F.B. Racing
01 WRX (STI badged)
2010 XR5 Focus
06 Impreza Hatch 2.0i