Slight roar from under the truck

[Aistinvc]

When driving at a constant speed when RPMs are around 1,500-2,000 there’s an obnoxious roaring like sound coming from the underbody sending a slight vibration through the cab I’m not sure if it from a bad brake or something wrong with my transmission or transfer case, both of which are from a different vehicle after my transmission seized. I’m just trying to figure out if the noise would go away if I swapped out my old transfer case with my current one.