Did you ever have this fixed? I just bought my 2012 premium used with only 18,000 miles on it. It has the same issue.
Had my vehicle serviced today at Ourisman Chevrolet/Buick/GMC in Alexandria, VA. I described my issue to the service agent. "Customer states when accelerating in reverse there is a loud squeaking noise when A/C is on after car has been driven." They did experience it and replaced the Belt 12653318 and Tensioner 12605175 under Warranty with no charge. 13,096 miles on my Regal right now.
Waited until I needed VA State Inspection, VA Emissions test, Oil Change, and Tire Rotation services done as well.
Dealt with five humans. Service Agent, Parts Counter, Cashier, Customer Service Rep (talked about upcoming survey), and the Person that drove my car up. All courteous and professional.
Bought a Buick Baseball Hat and a bottle of touch up paint while I was there. They now have a well stocked merchandise display that you can buy on the spot. Very nice touch. Lots of other AC Delco products as well for sale.
Hope this model is what is most GM Service Centers are going to move to. Great experience.