2001 GMC Sierra Whining Noise

[DAndrews]

Noise appears to be coming from under truck. Only happen when first taking off, usually for 2 to 3 miles. It then doesn't do it again until the truck sits for awhile and cools back down. I can't duplicate the noise when not moving.

[Badbird2000]

Can you tell if it's coming directly under the truck, or from the rear? My 2012 started making a whining noise from the rear. Turns out it was the pinion bearing. 215,000 miles. 

[DAndrews]

It doesn't seem to be from the rear.

[richard wysong]

Transmission more than likely, It's letting you know there worn parts , Unfortunatly  there is no fix other than tear down and rebuild. If it's 4wd you may luck out and have a transfer case problem.  common TC problems are low or no oil and oil pump wear, there are many things in the trans that can whine , Planetary gears, pump etc etc