Had the same issue, mechanic replaced the fan clutch and auxiliary belt.
The video's are posted here if you want to compare noises.
https://www.gm-trucks.com/forums/topic/261255-cold-start-whining-horn-like-noise-comes-and-goes-with-videosound-clip/#comment-2607383
Note there are multiple pages on the forum with the resolutions on page 2, getting a lot of follow up messages asking if the issue was resolved, but it's all posted here