Oil Pump??? Exhaust Back Pressure???

[Razzmaniac]

So this is about the 3rd time on the same subject. HA!! Apparently, im getting nowhere with the dealer.
2007 Xterra, 122k miles, loud Lifter knock when cold only and ONLY under load. (Not the typical typewriter clatter we all seem to experience) Not idle or warm. Sounds so bad like marbles dropping on a tile floor.
Was wondering now and read somewhere that the Oil Pump could be going bad or exhaust back pressure. My gauge shows normal oil pressure but this morning i did a test. I let the truck sit and warm up completely before driving it. I STILL had the loud lifter knock for quite a few miles of driving. Once its been actually driven a ways, theres no knock at all.
SOOO. . . . to add to it. I notice that when i first start up when cold, The exhaust under the truck smells really strong. I assume the Cats are in need of changing. ALSO read that back pressure when cold can cause weird things to happen in the engine.
Im at a loss because id hate to bring back to the dealer for him to tell me AGAIN that its normal wear on these engines.

HELP!!!!!!

 

[TJTJ]

You can simulate exhaust back pressure issues by blocking the exhaust with a rag, etc, while the engine is running, and seeing if the noise changes in character. If it does, then you know its at least related to the back pressure.

 

[Razzmaniac]

That might work BUT the noise only knocking only happens when the truck is under load, being driven. Not idling.
Do you think that would create the "under load" scenario?

 

[Razzmaniac]

WAIT!! How about "Piston Slap". Been reading about that the past half hour...