Okay, so I have a new Kumho 255/55/18 on the left rear. I am noticing a slight whine while coasting - just like the whine I get when i have a low air tire. The kumho definitely has more knobby tread.. my Nitto has the flat street design.

Next question: Do I buy another Kumho and run two new tires in the back with the Nittos on front, or do I buy a Nitto and replace the Kumho (leaving the Kumho as an emergency spare)? If the latter, would the truck react to a new Nitto and a used one on the back?