97 Buick Riv pinging & knocking

I've got a 97 Buick Riviera with 170,000 miles. It just recently starting pinging and knocking (usually when I am going up small inclines). Engine runs
smooth, engine temp seems normal, any ideas of cause or what I can do to stop it?
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Carbon buildup increasing compression ratio?

pinging and knocking (usually when I am going up small inclines). Engine runs smooth, engine temp seems normal, any ideas of cause or what I can do to stop it?

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