Engine Chirping noise when accelerating with the AC on

My vehicle is actually Chevrolet Captiva. The vehicle is making chirping noise while running air conditioner, when giving it gas. Seems to make the noise during lower acceleration and not higher acceleration. And seems to only do it while running air conditioner or heat. I have taken it to car service, where it was purchased, twice now, and both times, they have come back and said they cannot find anything wrong with it. But something is causing the noise. I believe their techs just do not know how to troubleshoot outside a diagnostic test. Any suggestions you have would be greatly appreciated. Thank you.