A/C noisy?

Today at the shop we saw the tensioner bouncing causing the belt to shake and squeal so we took a socket and ratchet and gave the tensioner a little more tension on the belt and turned the A/C on and put it in drive and even tapped the gas. It stops when you give the tensioner more tension so I guess the new tensioner I put on it months ago is defective. And or the new belt I put on months ago before then is stretched? Both are ACDelco OEM parts so I'm kind of confused but I guess I should change them again or warranty them out or try different brands?

Problem solved. I had an ACDelco 6k609 belt on it because rockauto said it works with A/C. I looked up on Chevrolet parts website and it calls for a gm55578115. Rockauto doesn't show that number as a cross reference when you select the 6k609. I bought a continental 4060610 which crossed to that 55578115... Delco 6k609 says its 61 1/2” and the 55578115 says its 61” so I guess I had the wrong belt on my car and I'm not sure why rockauto lists it as an option or why there is 2 different sizes that close in range for a with A/C option.