Old one >>1008351

Lately i havent been able to get my indexing right and i get crazy chain skipping. my friend told me my hanger was bent and he straightened it out (he is a bike mech btw, it was a minor bend so he could do it) I have also replaced my chain and shifter cables before and until 2 days ago it was fine. when i try to adjust it now i get a knocking noise from the rear and the chain goes up 2 on a certain cog. Also what would happen if i put some rusted dust caps from my jockey wheels in vinegar? I know that it would also remove the metals protective coat.