Lower end Knock?

[Unreal Summit]

So when I was checking my transmission the other day for anymore leaks I left the truck running. As I could hear a knock as my head got near the bottom of the truck I could hear a knock. Not like a rod knock not really sure what it was. I could hear it on the driver and passenger side. Couldn't hear anything up top. Is this normal?  I have never paid attention or been under one while it was running. 

[Dieselfuture]

Was the truck warmed up and did you just pull up without shutting it off or was it first start in the morning. 

Probably normal either way Cummins is clunky 

[Unreal Summit]

It was still pretty cool it had maybe ran for 10mins Max and hadn't drove but 60 foot.  Guess I should listen after it's warmed up some. I was kinda thinking it's normal cause they are so loud anyway.

[Dieselfuture]

When cold timing is advanced 

[Unreal Summit]

Yea i was thinking that would be more in the top side of things.