yeah, daahh
as usual, GM engineers and PR are quick to come up with another bs about "that's how it's supposed to be".
ok, you have pushrod engine or not? if yes, get used to that noise. it's typical for pushrod engines, as due to long pushrods, it takes time for hydraulic lifters to reach operating pressure and close gaps on rockers.
otherwise, if you are about 500 miles close to oil change, pour a can of Seafoam into cranckcase and drive on it. YES, I SAID drive on it, it's totally safe to do. it'll clean "carbon deposits" just fine.
they call it clunckerado for a reason. one thing i learned about this truck off MANY posts and my experiences. it's been designed by people that used to work for 19th century steam engine and carriages companies. everything got to be BIG and CONTINUOUSLY LUBRICATED. and clearencies are in tenths of inch, not of millimeter.
BIG. and a lot of GM magic lube. A LOT.