Here are some pictures… I believe it’s the Y belt. I have a taz4. I tightened the belt recently after repositioning it so that it’s horizontal with the stepper. When I purchased it it wasnt perfectly horizontal, and rubbed the clamp underneath. Also the design of the clamp seems to rub on the belt towards the back half of the bed. Im sure there is a fix for this.
The prints are not perfectly round on the bottom half of the printbed, aproximately 5mm in.