Hello.
So i though this would be the best section to put this, here it goes.
I have a 04 max, non HLSD. Problem im having is when i go into 3rd gear or above, i get this humming like noise only present if i coast, if i begin to accelerate hard or engine brake, its nonexistent. Ive uploaded a video of the noise here. This is in 3rd gear, its most noticeable while at 2.5K RPM, if i go to 4th its most noticeable at 2K RPM. As i go to 5th and 6th, its there but higher pitched. There is no noise at all in 1st or 2nd gear.

Ive checked the gear oil, its fine. When i drained gear oil for the first time when i got the car, it looked fine, slightly dirty but not a big deal. No metal shavings with the oil. I have amsoil GL4 in there right now. Shifts fine, no grinds or any issues with the shifting. Ive checked my axles, all good. Pretty sure its not the alternator, or the wheel bearings.

So, what could this be? Differential bearings?
Thanks.