Odd sound as H3 was being warmed up. Sounds like "bearings going out" type of sound. Good heat. This morning heard a rotating knockin noise as i revved up but went away.
Seemed like a temporary, slight loss off horsepower. 1qt low on oil.
Waterpump?

 

It is virtually implausible to expect a group of folks on a web forum to be able to guide you to a correct solution without all of the facts and stats. Even then it's a crap shoot.

 

If you were low on oil, you might have been hearing thirsty lifters.

From a 6 year old post of mine:
"The Atlas Series engine has hydraulically actuated timing chain tensioner that requires the oil pressure to first come up to add the required tension to the timing chain. Over time the chain will stretch, but the tensioner has ratches that will eventually allow it to click over to the next position to correct for the slack in the chain. Sort of like self adjusting brakes worked.

When you first start the cold engine, if the chain is loose and before the oil pressure can come up to take up the slack, the chain may contact the insides of the front cover. It sounds like a rattle that immediately goes away.

What is happening is the chain is loose enough to slap but not yet loose enough for the tensioner to click over to the next position. Not all will do this, but a bunch can for a while. If this persists for a long time, you may have a timing chain that stretched too far, or tensioners that are worn and need to be replaced.

GM TSB 06-06-01-017G covers the revised cylinder head and timing chain service procedures for these engines.

Many/most will tell you this is normal. I would say it is more expected than truly normal, but it is not a big deal IMHO. Life is good if this is all you are worried about."