Anyone have any idea what this transmission whine is?

[WWONG]

Hello all,

So I have a 2012 X5 xDrive35d that I custom ordered and purchased brand new four years ago. Warranty's gone and it is almost at 46k on the odo.

As luck would have it, two months after warranty, I start hearing this whining as I'm accelerating and I believe it is coming from the transmission. The sound increases and decreases as the RPMs go up and shifts. No noticeable decrease in vehicle performance and no lights on the dash.

The whine sounds like an electric golf cart or sometimes like a crying cat. It's most noticeable between gears 1-3. It happens when the vehicle is both cold and hot. The sound also happens if I lay off the gas approaching a red light and let it coast.

Does anyone have any idea what the heck this sound is? I'm hoping it's something simple (low ATF fluid?) that perhaps a transmission fluid change may fix. I've looked around on the underside of the car and my garage floor and have not found any indications of leaks.

Below is my video of the noise. I manually shifted so that the RPMs can go higher and it can be heard easier but it does it normally on D as well.

UPDATE: It was a bad idler pulley. See my post on Pg 3.