I can be sewing along and then hear this "clunking" noise to find a large clump of thread is left on the underside of my fabric from the bobbin. What can be causing this, I have re-inserted the bobbin many times.
I'm having the same problem, pseudoquilter. I sew about 2 feet on a straight seam, then hear the "clunk" and see a lot of threads in the bobbin area. I cleaned all the gunk around the bobbin area and rewound another bobbin. What I have done since has been working. Hopefully, it keeps on working or I think I will be looking for a new machine. Mine is pretty old. Maybe it's just a Michigan problem. LOL