I just got a 1998 2dr blazer with 197,000 miles and it has an engine knock. I have included a video of the blazer running so hopefully someone can narrow down the possible problems. I'm thinking its a connecting rod bearing but I could be wrong.
Sorry about the wind... I'll try to get another video soon...
http://www.youtube.com/watch?v=wOVoWSyxsfA

I just found more batteries for my camera! Less wind in this video..
http://www.youtube.com/watch?v=ol3dRTTp_Oc

 

*Bump*

 

Fan Clutch? Check your water pump dude!

 

you can try using a long screwdriver or something metal. hold one end on different places on the block and one to your ear.

one would think bearings would make noise at idle too

whats your oil pressure like?

 

My oil pressure is about 50. It does make the knocking noise at idle too. It's louder when the engine is warm.

 

then its time for a 5.7!!

 

Does it do it under a load?

 

It does it all the time.

 

A loose bolt on the flex plate will make a noise kind of like that.

 

a broken valve spring made same noise in a truck I had, put new one in ran fine!