Well, when I heard those noises... all I said was "Holy $h!t!!"

Definetly rotating assembly related. And yes, getting some feeler gauges and pulling the oil pan off is going to be the next step. Check your rod freeplay.

Also, loose flywheel bolts perhaps? Maybe there is a bolt flying around in the flywheel area? Pulling the tranny might not be a bad idea, just to check the condition of the clutch/flywheel assy.