I have a 2019 GMC AT4 6.2 with a noise at start-up that sounds like a bearing in one of the pulleys or belt tensioner is bad. I noticed it around the 3,000 mile mark. It is worse during cold starts and it is almost a squealing noise. I took it in to the dealership who had it for almost a week, and finally determined the noise was coming from the catalytic converters and there was nothing they could do about it. They even put the truck up on the lift and had me come in to listen to see if it was the same noise I was talking about. And yes the noise was actually coming from the catalytic converters. I guess this is normal but it really sucks! My 2017 Chevy Silverado that I traded in for the AT4 did not make any noise, just saying! Stan S.