I never carry anything in my bed
The truck has about 40k miles. It's very strange. I've asked a few people who wheel with their overland rack, tent, water jug etc and they haven't had this issue.
It's cracked right on the welds of both sides. It's not right at all lol. One day after work I go so tired of thr rattle sound I was hearing so i started shaking the bed, pushing up from under the truck and then I realized my tailgate had a lot of play so it was contributing to the rattle I was hearing. I took off the bed and the rattle reduced significantly, but it was still there. That's when I started looking at the bed very thoroughly and found those cracks. I got some footage of the wobble and sound with my gopro but I'm vacationing in Miami ATM... will post when I get back