My 2021 6.6 liter 2500 HD Silverado custom is currently in the dealer shop for this. I do not believe it is anything serious. My experience is backyard mechanic at best. But what I think is happening could most likely be one of 2 things. A tensioner pulley malfunction or a pulley misalignment. Tensioner pulley is quite an easy fix to do at home. Pulley misalignment does require some special tools. There are two pulleys installed on this engine from the manufacturer by mode of machine. Sometimes they press pulleys in to far or not far enough causing the belt to rub inside edge of one of the pulley's, causing the chirp you are hearing. If it’s under manufactured warranty still, and don’t mind not having your vehicle for a bit. Take it to dealer to have them troubleshoot.
