Took my plow truck to town today to get gas. Heard something vibrating on the way there and back from time to time. When I got home I left the truck idling and opened the hood. Turned out the rattling was the plow lights old and decrypt. But then I noticed what was either an engine knock or or something loose and moving and making a knocking sound. Went to the drivers side and raised the engine rpms and the noise went away, let it idle back down and the noise came back. Nonie seems to go away above idle. Had no problem with power or dive-ability on my way to and from town. Will check it out more tomorrow, my current health condition makes long standing or working difficult and painful. Checked oil it was clean and full and oil pressure was good. Noise seemed like it might have been a little louder on the passenger side. This is the 4.3l engine.Thanks for any and all info.
Bill

 

Without seeing & hearing it I’m thinking you have a lifter going bad to or an oil galley is getting clogged. The lifter isn’t “pumping up” because it is too weak, it’s getting gummed up inside, or it’s not getting enough oil.

If you have a Harbor Freight close by go purchased a cheap automotive stethoscope for a couple bucks. Put the tip on the block /intake and move around until you get the clearest sound. Raise and lower the RPM’s and see if you narrow the location down.

Noises tend to travel through other components leading you to believe that noise originates somewhere else. You could further narrow it down by removing that valve cover and checking valve lash cold then hot. You could also look & listen for that noise while it’s running with the valve cover off. While the valve cover is off & motor running you can look to make sure oil is getting up to each rocker arm.

Oil is supplied by the oil pump through the lifter galleys to each valve lifter. The lifter takes that oil for lubrication but also squirts some up through the hollow pushrod which’s spews it out on to the rockers and valve stems for both lubrication and cooling.