Strange sound after my transmission was replaced.

I own a 2023 silverado 1500 3.0 diesel. My truck sat on the dealership lot for almost 2 1/2 months, waiting for a valve body. Eventually, GM sent a replacement transmission to correct the issue.

I have had my truck for about two weeks now. When I accelerate from a stop, there is a faint metal rattling sound, which tends be loudest at the beginning of each gear change. The sound starts to dissipate the faster I go. Again, the sound is only present when accelerating. If I am driving at highway speeds or if I rev the engine in park….nothing. The best I example I can use to describe the sound is a metal washer vibrating on the bottom of a tin can. I have crawled underneath the truck a few times. I don’t notice any loose parts or heat shield damage.

Does anyone have any suggestions. I am in the process of trying to get it back to the dealership so they can hopefully diagnose the sound.