If you watch what's happening when the noise happens, you'll see that it's when the thread pulls between the bump on the bobbin basket, and the spring. It's right in the front, right side of the bobbin area. Usually, you can fix it by sanding off any rough spots on the bobbin basket. I use a very fine sandpaper - about 400 to 600 grit. It only takes a few gentle strokes. However, if the bobbin basket is too damaged it will need to be replaced.