I experienced the same noise. Had it in and out of the dealership several times. Picked it up today with a spacer inserted into the back of the leaf springs. See photo. Dealer says that this eliminated the noise. Chevy says that it's a known problem with the Colorado. I have a Silverado 1500 - 2018.
I have the same problem in my 2018 Silerado 4WD. Most noticeable when there is a load in the bed or when towing (tongue weight about 400#) It is currently at the dealer for the third time. Last visit they removed the bed to isolate that. Any ideas or solutions much appreciated.