Sounds like a collapsed lash adjuster. But there could be some exhaust leakage going on as well. Remove the cam cover (cold engine). The best thing to do is reach in and grab each follower just above the lash adjuster. Try and wobble/rock it from side to side. If the lash adjuster is collapsed the follower will move. Rotate the engine so the came is on the follower at it's lowest point (heel). The follower over the bad lash adj should then pop off using just your fingers if not use a screwdriver to flip it off. Take needle nose pliers and grip the lash adj while pulling it straight up and out. If the nose/tip of the lash adjuster drops down or stays in the collapsed position then it is defective. You should be able to push on the plunger and it stays hard with no movement. Drop a new adjuster in, replace the follower using a screwdriver and you are good to go. May be more than one bad adjuster so check them all while under there. Not sure how many miles you have on this engine but it sounds quite noisy overall. You may want to do a manual oil pressure check on it just to make sure your oil pressure is up spec. Low oil pressure or low oil volume will cause lash adjusters (and other components) to generate noise until they can get pumped up.

 

360,000 k on it...

 

have u figured out what your knock is?? my 4.6 is making pretty much the same noise, and it sounds like it is coming from the top end on the right bank like yours is, and it started doing it a few miles after i changed oils to.