The needle is either hitting the throat plate or quilting foot. The quilt is probably pulling the needle to one side and it's hitting something on the way to the bobbin. You need to have the quilt supported so there is no drag on it. You also need to "puddle" the quilt in the area you are sewing. If you have the single throat plate on (small round hole) switch to the zig zag throat plate. This will help the needle not to hit.