This is exactly the same problem that I had constantly with my Janome 6500. The bobbin jumped and rattled so badly that I put the needle right through the casing. My dealer refused to do anything and kept telling me it was "operator error" and implied that I just didn't know how to run the machine even though I had been sewing for more than 30 years. I finally found out about oiling the wick under the bobbin case when the rattling starts and this helps. After dealing with all it's issues, I would never buy another Janome or deal with my local dealers again and I went there because they had such a good customer reputation. Both of my Husqvarnas stitch rings around my Janome and didn't cost me nearly as much money or give me any of the hassle.