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. 

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 

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.

When cold timing is advanced 

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