I had the same Issue with my serpentine belt on my 2018 Infiniti Q50 Red sport after installing the z1 anti jump kit with Z1 belt . I had squealing still at idling once car was warmed up to temp , I fixed the issue by uninstalling the Z1 belt that z1 provided with the kit and switched it out with a Gates belt which is a way tighter belt to go on the pulleys , once I swapped that it fixed my issue right away no more squealing. Hope this helps 🙏🏻