2008 Trailblazer LT 4.2

I got a knocking sound coming from the engine. It is very loud when the engine first starts, but quits down after a few seconds and then you don't hear it unless you really get down on it. I disconnected the serpentine belt and knock is still there at start up. Sounds like a rod knock, but I'm not losing oil PSI. I carry 40 to 50 PSI hot or cold. Any ideas???

 

How many miles on your vehicle. Maybe post a vid so we can hear it

 

Possibly a sticking lifter.