[Joseph Upson]

That noise is most likely reversion (combustion gasses popping back into the intake. Premium fuel should make it stop, or not with the code. The direct injected 3.6L is sensitive to fueling and ignition/timing irregularities, which can be influenced by dirty intake valves.

 

[Joseph Upson]

Most likely this is a timing chain issue.

It's a contributor as it results in irregular timing consistency, but it (noise) can be present with old and new timing components and responds best in my experience to premium fuel and intake valve cleaning.

When GM was having trouble with these motors running out of oil because of long oil change intervals and forgetting to remind owners that the oil life monitor has nothing to do with the oil level and that it needed to be checked regularly, the affected cars would show up at the dealer running poorly and throwing cam codes along with others, because insufficient oil supply results in erratic cam angles. The OP hasn't clarified it, but the noise is very characteristic of the DI motor and the associated sensitivities. One in particular is the fact that DI motors don't handle rich fuel conditions well, which can cause the symptom experienced here. Cold startup is probably the richest condition the motor experiences under normal circumstances and that's one of the reasons the noise is usually only encountered during the first start of the day if it's cool.