Check your bobbin case to be sure there isn't a burr or hole in the edge of it. This is a common problem with some machines. It often happens when you break a needle. It that's the case, you can take a very, VERY, fine sandpaper and go over the burr until you can get to your dealer for a new bobbin case. This problem would definitely cause thread shredding. You may also want to watch the thread as it feed off of the spool to be sure it isn't getting hung up on something which would cause the shredding. Hope you find a fix soon.