This document shows how to check whether your motors need straightening or not. If they are only slightly crooked, this method will work. If they are grossly out of alignment, you will need to adjust the brackets screws, which is shown in another post.
The photos show only the X motor (the one that runs the length of the table) on my Gammill Premier. Check the Y motor in the same way. The photos show an original motor with the white gears, and a supermotor with the clear belt. Your motor may look slightly different but the mounting block will be the same. It is important to place the straight edge against the mounting block and not the motor cover.
Take the cover off the motor and place a straight edge against the mounting block that has the two set screws, as shown in the photos.