First, open it all up again and use your vacuum cleaner, which is a great way of getting rid of fuzz we cannot see or reach. There might be something tiny caught. Look at your bobbin case. Is there a ding or a gouge where the needle might have hit? Is the machine still making a noise while sewing or has that gone away? Did you try sewing with the same bobbin or a different one? I would try a different one just in case the bobbin got damaged in a way that cannot be seen easily. And if that doesn't solve the problem, then I would try adjusting the tension. If that doesn't work, well, it might be time to ask a professional.