Inspect your linear rails. Make sure there is a red stopper in the screw holes on each end of the linear rail. I would recommend you leave these in until you're ready to mount them to the frame

The carriage should slide along the rail with little force required. I don't have the preload information on these but it's not uncommon to have to apply slight downward force on the carriage for it to slide smoothly

There should be a small gap on the along the bearing channel

Teardown