3rd Gen Taco making high pitched sound from rear

Just opened my rear sliding window and noticed a high pitch sound when I hit 40-50mph coming from the rear. The faster I drive the faster the sound and vise versa. Sounds like a power steering pump needing to be replaced but not as loud. When I park the truck and leave it running, nothing is out of the ordinary. I’m afraid if it may pertain to the differential? Any ideas?

 

Did some research and YouTubing. Found out that a lot of people were having the same kind of "howling" noise and that it MAY be from the Rear Diff. Has anyone had the same issues and been able to find a fix? I still have warranty on the truck, but I'm concerned the dealership/Toyota will just say they don't hear it.