I would take that cover off and at least inspect it. A tiny piece of thread in the upper area costs me $125. Now I know how to get that top off and check it myself. I have two Brother sewing machines and a couple of older Singers. It sounds to me like you don't have any tension on your thread. Have you checked your tension discs. I have seen it recommended that you floss the tension discs with dental floss. Haven't tried it myself.