Whining Noise In 2007 Sierra 1500 Cc 4wd

[boatr01]

I have a 2007 Sierra 1500 CC 4WD that I purchased new. It has 53k miles on it, and has recently begun making a whining noise after I start the truck. The noise has gotten progressively worse with respect to the duration. It only does it when the truck is cold, and dissipates over time. It occurs immediately after starting for a short period of time, while the truck is not moving. After it dissipates (15-20 seconds), and I put the truck in gear, it starts again. It usially stops, and then might start up again while I am accelerating after driving for a block or so. I have been under the hoo, and under the truck after starting, and cannot pinpoint where it is coming from. It eventually stops after the truck is warm. The duration of each of the above sequence of events sems to be increasing over time (?).

 

Thanks for any ideas.

 

Eric