Originally Posted by
PaperPrincess
Sounds like backlash. The bobbin spins a bit too fast, making a loop which wraps around the shaft. It seems to occur more when the bobbin is less than full. I would try bobbin genies
http://www.youtube.com/watch?v=Hdo_q0M2rsw
that at would be my guess too. If there is a backlash spring in the bobbin case you could adjust it up a little.
I had that problem on my Sweet Sixteen....