Man I was hoping it was something simple like the exhaust vibrating on the frame, not the crank!

 

Just rule it out with a simple check using an indicator.
An oil analysis can also tell, if you have excessive metals in your oil.

 

I haven't torn into mine yet. Unsure if this truck will see the road, or become and engine donor. But before either happens... the endplay will be something i'll check for sure. Timing cover will come off for inspection and KDP. Check out the vac pump thoroughly at the same time.

 

That's what it sounds like to me. Just the gears slapping against each other at low idle. I wouldn't worry about it until something comes through the case. My G360 makes a similar sound when it's in 4th below 1500 rpm. The cluster gear has no load and is slapping things around. Hopefully some of that noise will go away when I get the trans swapped out on Friday.

Edwin