I having this issue forever and have tried most almost everything i've found on the internet. In the picture you can see what i'm talking about. It happens more toward the front of the bed and also on the outer parts of the bed.This issue is also leading to an uneven surface in Z.Anyone know whats causing this? I feel it may be a mechanical issue. I made sure to tighten the belt using a freq tuner app. so should be good on that end. IMG_0720.jpg