how to tell if I have a knock

[Dodgecrawler2011]

Kinda new to this cummins stuff but. When the truck Is at idle it all sounds normal. But when u rev it a bit it kinda has a knock sound comeing from the back of the engine. Its only when u touch the throttle and goes away Instatilly. Also I pulled the timing cover off to checl the kdp and its gone. Theres signs that it fell out and made some scrathces on the cover. Should I drop the pan I get it out.

[directinjktn1stgen]

its to heavy to get picked up in the oil strainer and far to big to fit through it i wouldnt worry with it may fall out upon your next oil change if hasnt already

[apexfd]

I was glad to find my KDP had not budged.. Although my truck has a bit of a knock, I think its worn injectors.