Marvel Mystery Oil is used to loosen up deposits and clean the gunk out of the nitty gritty places yes?
So things that were tight may now be a skosh looser because of gunk loosening up and so my guess is it's an oil return line loosened up by MMO and being hit by the crank as #3 spins past.
Or maybe that's just because that was where my mystery knock ended up coming from
I found the key to using video is using the editing software to identify
on the sound track where the knock happens and then compare engine component positions in those frames...
