Thanks for posting and I watched/listened several times (after fixing your link).
Since you didn't capture the sound that you reported, kind of hard to diagnose anything on that.
I will note that it seemed like your oil feed assembly that rides at the center of the rocker shafts seems to actually move and jump around (more up and down than side to side) and seemed there might have been some similar movement with the rocker shafts/stands.
To my knowledge those shouldn't be moving around and would suggest checking your rocker stand bolts to make sure everything is tight/secure and that your rocker shafts aren't actually moving (they could be badly worn which could account for movement in the stands).
If you have a distinct intermittent noise rumbling around down low, next step can only be to drop the pan to investigate.
Dan
