I bought a 4.16 tranfergear box (rocky road) that was supose to fix my lack of power with 31" tires. at first it seem to work but now it sounds like the gears are rolling inside . should I have changed the ring and pinion at the same time ,and would  this stop the noise? there is less than 400 miles on it.what could this be?

drain oil, look for metal, report back findings...