It's Chains, Tensioners, etc. Galore! At least they're all on one end unlike that terrible 4.0 Ford.
I tried some lookups, and it seems this V6is "Northstar V8 Family." The site I found this pic on calls the engine "interference." And includes a warning to STOP DRIVING the car once the noises start. I hope my notes here acknowledge northstarperformance adequately and don't violate somebody else.
Interference of valves hitting top of pistons when out of mechanical time. Be prepared for the worst. BENT VALVES.....Yikes..
Check that the exhaust is not plugged. Take out O2 sensors and see if it does the same.
In regards to JD's post, you will notice 1 primary chain tensioner, and two secondary one also, and of important note here, all oil pressure loaded.
So if you do attack the chain in this beast of modern marvel, you may want to do an engine flush, BEFORE. That way, you will go in there maybe seeing it clean, and maybe those oil passages for the tensioners, will have a fighting chance to not skip time again, if that is in fact the case.
When you open one of these commadores up, you will notice if the client used the proper oil. HIGHLY recommended by gm to not use anything else but 5w30 in these and if you use cheap oil, you will notice the inside cooks quick cuz these like to run hotter than normal and that will eventually gum up your VVT cam actuators.
Here is a pristine example of what I am talking about. This engine had no chance in hell of making a high mileadge engine due to obvious lack of maintenance.
The VZ engine is nice when it is well maintained, but they go south quick once you loose track of maintenance.
These engines remind me of the 3.6's dodge is pushing out lately. Boy do those suck large. Now mind you, the only ones I have actually torn into, are police interceptors, so tons of idle time with frequents bouts of go daddy go type driving. but I bet my dime on a dollar that dodge is going to be paying some techs some overtime in the near future.
Square cam on cyl five seems to be something that will be a favorite. One thing I know for sure, I won't be seeing those v6's doing 400 to 500k km's. For that to happen, you need to have worked on a few caddies to know, if you put in normal mineral oil, your screwed from the get go.