3.8L engine starts to ping recently under load

I have a 3.8L 1993 SSEi that starts to ping when the engine is hot and under load. It does not ping very loud, I only notice when I step on the gas pedal hard or driving between walls (such as tunnel). I use correct gas
that is 91 octane. Car drive and feel normal. All fluids level is where they should be. Any ideas?
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Look for carboned up or inop egr valve first

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check the plugs

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