i am sure there could be a number of causes, but i can share one thing that happened with my Viper. there is a blue stem that you push on to unlock the print head carriage to move it. at the bottom of it, it comes to a T and there are two cylindrical tubes. When you push it down, the tube on the right has a spring-loaded white plunger that goes down, and is supposed to pop back up. On my Viper, the white plunger stayed down and was catching on the frame of the capping station area. i removed the white plunger and cleaned and filed it so it moved up and down smoothly in the tube. That took care of my problem, except that some of the gear teeth had gotten out of sync when they made the grindig noise. I moved a gear slightly with a screwdriver and it then worked. the gear I moved was on the right side behind the spit station.