Hey Laverne,
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first I would check if the Z ball screw coupler is loose. How to reattach it is shown in this video. It shows it on X or Y Axes, but with Z Axis it is similar, with the difference that the coupler is better accessible, as can be seen on this video . Unlike on the other axes, on Z axis, the ball screw does not need to be removed in order to fix coupler screw! The stepper motor shaft has a flat part. Make sure the black grub screw is tightening against the flat part of stepper motor shaft.
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then I would check if Z Ball Nut Set Screws are loose.
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finally I would check if there is a wood dust-oil mix inside the Z ball nut. This is point 5) in this FAQ document. There is a link to a video too.