Most engines with hydraulic valve lifters make some clattering noise during warmup. This is rather harmless, unless it persist after the a few minutes and when warmed up. Yes, an equivalent 5W30 dino oil is thicker than synthetic at very low tempertures (they are equal at 0 Celsius), and flows slower. So your 5W30 synthetic is probably the best compromise. If it takes only a minute or so for the noise to disappear, you're OK, the engine is not in danger. If the ticking persists, you should have it fixed for sure. Sometimes you can get this noise if the lifters are sticking because of not enough oil changes. In that case, the noise would persist, but could possibly be cured with a can of valve lifter additive. GM used to sell it themselves. But, I assune you have maintained the vehicle well.
I have not replaced a lifter for a long time, so you would have to get a quote. (Best go to an independent shop who know GM engines. The dealer would charge you a fortune.) It's done after removing the intake manifold, which then allows access to the valve gear. The lifters themselves are cheap.
Since you have little to lose, you can try a can of valve lifter additive, and see if it makes any difference.