Yes, that's quite normal on the 2.7 Turbomax. This engine tends to be noisier at idle than the older 5.3 V8s, mainly due to the direct injection and the turbo, which give it a more "clattering" and mechanical sound.
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Honestly, the dealer's price seems high, but not completely out of line for a 2021 Denali with a complete front and rear brake rotor and pad replacement. At a good independent garage, many people would pay between $900 and $1,300 for the same job with quality parts. So at $1,700, you're clearly paying the "dealer tax."
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