If the whine gets progressively worse with speed, under load only (foot on-the-accelerator) and goes away when you are off-the-accelerator, it's more than likely the pinion bearing and maybe axle bearings. I had 8K miles on my 2012 GT and had warranty repair for my rear end where they replaced the pinion and axle bearings due to loud whine. At 65+ mph the noise was to the point where a normal conversation could not take place in the front seat. See what conditions exist when noise is "on" versus "off". Report back. Make sure to test it under load, cornering, highway speeds, when it starts, how loud it gets over time, etc. Check TrueDelta.com for instances of that. I found some instances of pinion bearing issues there when I posted my update on TrueDelta.