When your needle goes down, the hook system on your sewing machine creates a loop to form a stitch. If this does not happen, your hook timing is off. Sometimes a knocking noise can indicate a problem with your hook. The Singer 4423 Sewing Machine is an impressive, heavy-duty metal framed machine with a powerful motor, an electronic needle threader, and several other distinctive features. It has a really fast speed that can stitch all kinds of fabric, namely heavy fabrics such as upholstery, cotton, and leather, sewed plain buttonholes, and even carried out.