its probably one of three things and it kind of depends on how loud it is to determine whats wrong without taking the rearend apart.

the gears probably werent set up just right. theyre not loaded across each other at the right angle which is causing an uneven load and noise. this isnt good cause if you put a bunch of stress on it (hooking hard) itll probably tear some teeth off the pinion.

if its not too loud, it might just be the gear. aftermarket gears have a higher nickel content to strengthen them which can make them a little whiney. mine whine a little bit and i was there to confirm they were set to exact specs from Strange. just get some long tubes and drown out the noise

another thing it could be is that you need some limited slip additive in the rear end casing. i dont see anyone that is the least bit experienced with gears forgetting to add LSD additive to the rear end fluid, but i guess shit happens sometimes. pull the cover off the rear end and drain the fluid, look for any cracked gear teeth or metal shavings in it. replace the cover gasket and refill with the right mixture of rear end fluid and limited slip additive.

hope that helps