I have a 1988 chevy s10 blazer with 177xxx miles i started it up and noticed it was knocking. The knock isnt present in the first minute or two then appears when warmed up. The knock is constant and gets noticeably louder under load and increases and decreases with rpm. But when at idle and rpms drop it will faded away and then come back. The knock with go away randomly for a second or two then come back. i did an oil change and put a quart of rislone in it but nothing seems to help.

spun bearing?? bent push rod??

Here's a video
Rod knock? - YouTube

 

Knock at the top end will most likely be a collapsed lifter (Hydraulic not solid), Knock on the lower end will most likely be a connecting rod (Usually a double knock sound). You can always try running a heavier viscosity oil to reduce the knock. You can replace lifters by removing the intake manifold and the valve covers and removing each rod and removing the lifter from the bore. Rod knock is something you will either have live with or do a major repair. I had a 318 with a rod knock and drove it for a very long time.

 

That"s a connecting rod knock for sure