yep, right when the trans shifts it knocks. Basically when there is little load on the engine and the revs are around 2-3000. Had this happen a couple of times. Ended up to be a weak oil pump (spring was bad not holding enough psi).
The fact that #1 is black would make me think a different problem. Hope you dont have to dig to deep and come up with maybes
Just having 15000 should not need ridge reamer.