[GM man]

As a rule, I'm not a big believer in oil additives, but recently my mechanic recommended I try a bottle of Rev X additive. It's expensive ($35 for 4oz bottle) but it worked wonders for me. Put it in a Ford with 3.5 ecoboost with over 250k miles and cold start up was very loud. Now it's silent. Since then I've put it in all my vehicles. No lifter noise from my wife's 5.3 anymore. You might give it a try.