I have 3 new Singers but I don't have that one. I thought that maybe you were using the Simplicity bobbin winder. When I used that, I always had problems with the bobbin on my L500. I was using the Simplicity bobbin winder just as a convenience--winding a bunch of bobbins at once for all the machines so I wouldn't have to stop sewing to wind bobbins. Inspect your bobbins closely and see if there are any nicks or cracks in them. I had a problem once and when I looked there were minute cracks in it as if I had somehow wound the bobbin too full. Don't know how it happened but when I changed to another bobbin it was fine. My CE250 was making a racket once but that was because I hadn't cleaned the bobbin area in a while. Once I cleaned all the dust out and oiled the hook it worked perfectly! I've never had a problem using any particular thread unless I am FMQ'g.