Sorry to be rude, but make sure if you are going to ask a question to include printer make, mechanics, or other relevant info.
Assuming you have a Cartesian machine such as the prusa i3 you could have insufficient belt tension, a loose drive pulley, or a improperly tuned driver.
Prusa i3 Rework - Ramps 1.4 - E3d Lite6 - Full Graphic LCD Controller