It sounds like my 7.4. I cant tell which lifter it is??? I did the Marvel Mystery Oil trick. 2 Qts of MMO with 5 Qts oil and ran it for a couple hundred miles and changed the oil. The noise decreased by around 70%. I didn't see much gunk come out of the after change. It still does it when its been parked for a few days without driving it or it gets cold but when it warms up it almost goes away but I still hear it tho.
My worse case scenario is that I have to replace my cam and lifters. Aghhhhh

 

Take the value cover off and check your rockers with someone cranking the engine if the arms aren't moving it's definitely a lifter. Or if you can stop the arm from moving with a hammer handle pressed against the rocker arm. And it's always a good thing to check your bearings down below if cam lobe dammage is excessive. I've seen damage in mains and oil pump because of lifters in the dod ls