I had noises both before and after the diff install. Turns out the rear diff mount and both subframe bushings were trashed. Fixed those as well as the control arm bushings while I was back there and it's totally silent now. The diff went right in, no issues until I reinspected everything about a month later and found the lh axle seal leaking. Thinking I might have messed it up when I installed it in the case, I cleaned it all off and while turning the axles to further clean, noticed something odd on that side. The axles both sit the same length into the diff and the snap rings feel fully engaged. However, when turning the drive shaft, the left axle pushes out of the diff slightly, which is what I think is causing the leak, the axle moving away from the sealing surface of the seal. I'm going to investigate further, I hope I don't have to pull the OBX back out and fix something in the side gear.