Buy a new tensioner assy which includes a new pulley. They can wear out, jump up/down and cause your knocking sound. Ask me how I know.
......

 

Almost guarantee nothing related to the tensioner or anything else external or ignition of oil thickness etc. mine sounds exactly the same. I tried everything, exact same symptoms as yours. Only at temp, goes away with RPMs etc.

 

Only counts in horseshoes.

 

Lol guess your right.

 

Well it doesn't matter if the tensioner is the cause of the knock or not, it's bad and needs to be replaced. Just ordered the Gates tensioner assembly on Amazon. I took the belt off and ran the truck for about 30 seconds, I don't think I heard it anymore. Attached is a clip from the same location, no belt. Engine was at operating temp, probably a little higher because the water pump wasn't moving.

I still have a hard time believing that it has a slipped liner because the head gaskets were replaced very recently by an LR specialist so I'm pretty sure that they would've checked for slipped liners. Not ruling it out though.

Number9, I missed your first question. The knock does stop a few times. No editing tricks or recording issues, that's just how it usually sounds.

Tensioner is supposed to arrive on Tuesday so I'll install it then and report back. Thanks everyone.

 

Looked back at the PNs you mentioned and see you were going with the assembly rather than just a pulley.

The tick pausing was similar to what I heard when mine was bad, was able to see it jump with a close look and light.

Good luck.
......

 

Replaced the tensioner assembly today and now it sounds exactly how it did with no belt. I noticed the crankshaft pulley wobbles a bit, so I have a feeling that's what wore out the tensioner. It was a Dayco unit, not sure if that's the original or not. Thanks number9, looks like you were correct. Only thing is that I think I have to replace the crankshaft pulley in the future. But the noise is gone from what I can tell. I post a sound clip soon.