Mine whines. Always has.

I work at a car dealership, and each year we pull a brand new Silverado 2500 HD off of our lot and mount a snow plow to it. I do the plowing.

Each truck since 2009, when I started working there, has whined a bit in 4 High when driving down the road. Brand new trucks with 5 to 10 miles on them.

It's because the gears in the front end are more straight cut.

Same reason it whines when you go fast in reverse.