05 X3 E83 Rear Noise Sound

[achew111]

I'm trying to diagnose and fix an annoying sound. It is a two tone rapidly alternating mid pitch sound coming from the rear of the car. It is hard to pinpoint the exact location as it resonates throughout the rear of the car. It doesn't start until 35mph and gets louder at higher speeds. There is a 70-75 mph range where it goes away. It is present on acceleration and deceleration except for in that 70-75 mph zone.

In the video, there are two sounds. The first is a constant a metallic sound that is coming from the rear diff (I've been told that this is normal, but correct me if I am wrong). The second is the two tone rapidly alternating sound that I'm trying to figure out. I'm thinking it could either be the wheel bearings (no difference on curves) or the rear diff since that is also making noise (the noise doesn't emanate from the space place as the rear diff noise though).

I recently installed a rebuilt transfer case and driveshaft with a new guibo and center support bearing. Any help would be extremely helpful.

https://www.youtube.com/watch?v=0eg3Nu0LrIk

[Auto Parts Guy]

Have you checked the rear diff fluid? Diff noise isn't normal, at least in my opinion.