My Janome 6500 (has been serviced numerous times) does exactly the same thing. It has been terrible to munch up fabric, veers off seam lines if it hits a seam intersection and the feed dogs have always been set too low and at a sloping down angle at the back. As a result, I have hated this machine and wouldn't recommend a Janome to anyone. I know there are many users out there who love this machine but my Juki just sews so much better and was only half the price. I hope you have better luck getting this issue resolved than I have had.