I just did a gear swap on my 2013 F150 with a 9.75" axle. The gears are SVL (Aftermarket Dana parts), the bearings and races are all new, Koyo pinion bearings, Timken carrier bearings.

Final specs are:
Pinion preload: 25 in/ lbs
Backlash: .012" (max allowable)

The whining is light, but it's definitely there. You can hear it during cruise (but not acceleration), but especially upon deceleration. If you've got the radio on, you wouldn't notice it, but I know this isn't right.

Here are some shots of the final patterns:







Any input is appreciated.

 

It could be the gears themselves.

 

What ratio? What are you using for lube?

 

4.10 ratio, using cheap 85w-140 for breakin.

 

Some aftermarket gears make a little noise, especially in the higher numeric ratios. It's been a few years, but Richmond Gear used to state that 4.10 and higher numeric ratios will make some noise. I think most shops that replace diff gears will not guarantee that they will be noise free.