Singer Quantum XL 3400

Question

I have a singer Quantum XL 3400. Every so often when I first start to sew, after 2-3 stitches there will be a loud clang and the needle will jump to the right and there will be a clob of thread underneath the material. Right now I am sewing small squares together to make a quilt square. This will occur every 6-8 starts. It only occurs during a start and never occurs if I am sewing a long seam. The tension seems correct as the top and bottom stitching lay flat and snug to the material. I have checked the threading of the machine and the bobbin and they are correct. I took the plate off and the bobbin holder out and cleaned the area. What could be causing this? What else can I do?