If you are hearing a clacking sound & it sounds kind of like plastic it is probably your bobbin bouncing up & down. Had that problem with my 7700- have discovered that the wrong size bobbin is in. There are L-style bobbins & Class 15/A style, & almost all the Janomes use a Class 15, it is wider than the L-Style. For more information & locating the bobbin to fit your machines I have included this link.
http://www.superiorthreads.com/educa...phics/bobbins/
Hope this helps